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1. Discuss the history of DNA and the advancements of the past 20 years. Be sure to discuss collection methods, specific examinations conducted on the evidence (PCR, etc.), and future technologies currently being looked at.

A minimum of 250 words and two scholarly sources. Must be in APA format and referenced in APA format


Case Study: Use the Internet and Chapter 15 of your text to research convicted murderer Timothy McVeigh.

2. Case Summary

In a narrative format, discuss the key facts and critical issues presented in the case.

3. Case Analysis

Give a detailed summary of the forensic investigation's findings along with the evidence against Mr. McVeigh.

4. Executive Decisions

As lead investigator, prepare a summary for the prosecutor that explains the types of explosives used and their design and detonation.

All answers must be cited in APA format and referenced in APA format a minimum of 1,200 words ( total assignment ) and three scholarly sources. Please remember the In text Citations. Number 1 will be separate from then 2-4. Number 1 needs 250 minimum word count with two sources. References do not count towards word count.

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chapter 15 DNA: the indispensable forensic science tool Learning Objectives S M I T H , J After studying this chapter you should be able to: Ohow they are t Name the parts of a nucleotide and explain linked together to form DNA S t Understand the concept of base pairing asHit relates to the double-helix structure of DNA U t Contrast DNA strands that code for the production of proteins A with strands that contain repeating base sequences t Explain the technology of polymerase chain reaction (PCR) 6 and how it applies to forensic DNA typing 8 9 t Understand the structure of an STR 0 t Describe the difference between nuclear and B mitochondrial DNA U t Understand the concept of electrophoresis t Understand the use of DNA computerized databases in criminal investigation ISBN: 978-1-323-16745-8 t List the necessary procedures for the proper preservation of bloodstained evidence for laboratory DNA analysis KEY TERMS amelogenin gene amino acids buccal cells chromosome complementary base pairing deoxyribonucleic acid (DNA) electrophoresis epithelial cells human genome hybridization low copy number mitochondria multiplexing nucleotide picogram polymer polymerase chain reaction (PCR) primer proteins replication restriction fragment length polymorphisms (RFLPs) sequencing short tandem repeat (STR) substrate control tandem repeat touch DNA Y-STRs Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. 378 CHAPTER 15 deoxyribonucleic acid (DNA) The molecules carrying the body’s genetic information; DNA is double stranded in the shape of a double helix. chromosome A rodlike structure in the cell nucleus, along which the genes are located; it is composed of DNA surrounded by other material, mainly proteins. polymer A substance composed of a large number of atoms; these atoms are usually arranged in repeating units, or monomers. nucleotide The unit of DNA consisting of one of four bases—adenine, guanine, cytosine, or thymine—attached to a phosphate–sugar group. The discovery of deoxyribonucleic acid (DNA), the deciphering of its structure, and the decoding of its genetic information were turning points in our understanding of the underlying concepts of inheritance. Now, with incredible speed, as molecular biologists unravel the basic structure of genes, we can create new products through genetic engineering and develop diagnostic tools and treatments for genetic disorders. For a number of years, these developments were of seemingly peripheral interest to forensic scientists. All that changed when, in 1985, what started out as a more or less routine investigation into the structure of a human gene led to the discovery that portions of the DNA structure of certain genes are as unique to each individual as fingerprints. Alec Jeffreys and his colleagues at Leicester University, England, who were responsible for these revelations, named the process for isolating and reading these DNA markers DNA fingerprinting. As researchers uncovered new approaches and variations to the original Jeffreys technique, the terms DNA profiling and DNA typing came to be applied to describe this relatively new technology. This discovery caught the imagination of the forensic science community because forensic scientists have long desired to link with certainty biological evidence such as blood, semen, hair, or tissue to a single individual.S Although conventional testing procedures had gone a long way toward narrowing the source of biological materials, individualization remained an elusive goal. Now DNA typing has allowed M forensic scientists to accomplish this goal. The technique is still relatively new, but in the few years I since its introduction, DNA typing has become routine in public crime laboratories and has been made available to interested parties through the services of a number of skilled private T laboratories. In the United States, courts have overwhelmingly admitted DNA evidence and accepted H the reliability of its scientific underpinnings. , A What Is DNA? S P G S P T S P C S P 8 Structure of DNA 9 Before examining the implications 0 of Watson and Crick’s discovery, let’s see how DNA is constructed. DNA is a polymer. As we will learn in Chapter 12, a polymer is a very large molecule B units. made by linking a series of repeating U the repeating units are known as nucleotides. A nucleotide NUCLEOTIDES In the case of DNA, is composed of a sugar molecule, a phosphorus-containing group, and a nitrogen-containing molecule called a base. Figure 15–1 shows how nucleotides can be strung together to form a DNA strand. In this figure, S designates the sugar component, which is joined with a phosphate group to form the backbone of the DNA strand. Projecting from the backbone are the bases. The key to understanding how DNA works is to appreciate the fact that only four types of bases are associated with DNA: adenine, cytosine, guanine, and thymine. To simplify our discussion of DNA, we will designate each of these bases by the first letter of their names. Hence, A will stand for adenine, C will stand for cytosine, G will stand for guanine, and T will represent thymine. Again, notice in Figure 15–1 how the bases project from the backbone of DNA. Also, although this figure shows a DNA strand of four bases, keep in mind that in theory there is no limit to the length of the DNA strand; in fact, a DNA strand can be composed of a long chain with millions of bases. The information just discussed was well known to Watson and Crick by Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. ISBN: 978-1-323-16745-8 FIGURE 15–1 How nucleotides can be linked to form a DNA strand. S designates the sugar component, which is joined with phosphate groups (P) to form the backbone of DNA. Projecting from the backbone are four bases: A, adenine; G, guanine; T, thymine; and C, cytosine. J Inside each of 60 trillion cells in the human body are strands of genetic material called chromosomes. Arranged alongOthe chromosomes, like beads on a thread, are nearly 25,000 genes. The gene is the fundamental unit of heredity. It instructs the body cells to make proteins S that determine everything from hair color to our susceptibility to diseases. Each gene is actually composed of DNA specifically H designed to carry out a single body function. Interestingly, although DNA was first discovered in 1868, scientists were slow to understand U and appreciate its fundamental role in inheritance. Painstakingly, researchers developed evidence A by which genetic instructions are passed from one generathat DNA was probably the substance tion to the next. But the major breakthrough in comprehending how DNA works did not occur until the early 1950s, when two researchers, James Watson and Francis Crick, deduced the struc6 is an extraordinary molecule skillfully designed to carry out ture of DNA. It turns out that DNA the task of controlling the genetic traits of all living cells, plant and animal. DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL 379 the time they set about detailing the structure of DNA. Their efforts led to the discovery that the DNA molecule is actually composed of two DNA strands coiled into a double helix. This can be thought of as resembling two wires twisted around each other. As these researchers manipulated scale models of DNA strands, they realized that the only way the bases on each strand could be properly aligned with each other in a double-helix configuration was to place base A opposite T and G opposite C. Watson and Crick had solved the puzzle of the double helix and presented the world with a simple but elegant picture of DNA (see Figure 15–2). COMPLEMENTARY BASE PAIRING The only arrangement possible in the double-helix configuration was the pairing of bases A to T and G to C, a concept that has become known as complementary base pairing. Although A–T and G–C pairs are always required, there are no restrictions on how the bases are to be sequenced on a DNA strand. Thus, one can observe the sequences T–A–T–T or G–T–A–A or G–T–C–A. When these sequences are joined with their complements in a double-helix configuration, they pair as follows: T A T T | | | | A T A A complementary base pairing The specific pairing of base A with T and base G with C in double-stranded DNA. G S T C A | | | | M C A G T G T A A | | | | C A T T I Any base can follow another on a DNA strand, which means that the possible number of difT human chromosome has ferent sequence combinations is staggering! Consider that the average DNA containing 100 million base pairs. All of the human chromosomes taken together contain H about 3 billion base pairs. From these numbers, we can begin to appreciate the diversity of DNA , J O S H U A G A S P C S G S P P S C T 6 8 9 0 B S UP T A S P ISBN: 978-1-323-16745-8 P S G C S FIGURE 15–2 A representation of a DNA double helix. Notice how bases G and C pair with each other, as do bases A and T. This is the only arrangement in which two DNA strands can align with each other in a double-helix configuration. Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. 380 CHAPTER 15 WEBEXTRA 15.1 and hence the diversity of living organisms. DNA is like a book of instructions. The alphabet used to create the book is simple enough: A, T, G, and C. The order in which these letters are arranged defines the role and function of a DNA molecule. What Is DNA? DNA at Work proteins Polymers of amino acids that play basic roles in the structures and functions of living things. amino acids The building blocks of proteins; there are twenty common amino acids; amino acids are linked to form a protein; the types of amino acids and the order in which they’re linked determine the character of each protein. Normal hemoglobin Sickle-cell hemoglobin 1 valine valine 2 histidine histidine 3 leucine leucine 4 threonine threonine 5 proline proline 6 glutamate valine 7 glutamate glutamate (a) (b) FIGURE 15–3 (a) A string of amino acids composes one of the protein chains of hemoglobin. (b) Substitution of just one amino acid for another in the protein chain results in sickle-cell hemoglobin. The inheritable traits that are controlled by DNA arise out of its ability to direct the production of complex molecules called proteins. Proteins are actually made by linking a combination of amino acids. Although thousands of proteins exist, they can all be derived from a combination of up to 20 known amino acids. The sequence of amino acids in a protein chain determines the shape and function of the protein. Let’s look at one example: The protein hemoglobin is found in our red blood cells. It carries oxygen to our body cells and removes carbon dioxide from these cells. One of the four amino acid chains of “normal” hemoglobin is shown in Figure 15–3(a). Studies of individuals with sickle-cell anemia show that this inheritable disorder arises from the presence of “abnormal” hemoglobin S in their red blood cells. An amino acid chain for “abnormal” hemoglobin is shown in Figure 15–3(b). Note that the sole difference between “normal” and M arises from the substitution of one amino acid for another “abnormal” or sickle-cell hemoglobin in the protein chain. I The genetic information that determines the amino acid sequence for every protein manufactured in the human body is T stored in DNA in a genetic code that relies on the sequence of bases along the DNA strand. The Halphabet of DNA is simple—A, T, G, and C—but the key to deciphering the genetic code is to know that each amino acid is coded by a sequence of three bases. , Thus, the amino acid alanine is coded by the combination C–G–T; the amino acid aspartate is coded by the combination C–T–A; and the amino acid phenylalanine is coded by the combination A–A–A. With this code in hand, we can now see how the amino acid sequence in a protein J chain is determined by the structure of DNA. Consider the DNA segment O S The triplet code contained within this segment translates into H – [C–T–A] – [A–A–T] – [C–G–T] [C–G–T] alanine U aspartate phenylalanine alanine or the protein chain A –C–G–T–C–T–A–A–A–A–C–G–T– alanine aspartate phenylalanine alanine 6 Interestingly, this code is not restricted to humans. Almost all living cells studied to date use the same genetic code as the language of protein synthesis.1 8 If we look at the difference between “normal” and sickle-cell hemoglobin (see Figure 15–3), 9 by substituting one amino acid (valine) for another (glutawe see that the latter is formed mate). Within the DNA segment 0 that codes for the production of normal hemoglobin, the letter sequence is B –[C–C–T]–[G–A–G]–[G–A–G]– Uproline glutamate glutamate Individuals with sickle-cell disease carry the sequence –[C–C–T]–[G–T–G]–[G–A–G]– proline valine glutamate 1 Instructions for assembling proteins are actually carried from DNA to another region of the cell by ribonucleic acid (RNA). RNA is directly involved in the assembly of the protein using the genetic code it received from DNA. Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. ISBN: 978-1-323-16745-8 Thus, we see that a single base or letter change (T has been substituted for A in valine) is the underlying cause of sickle-cell anemia, demonstrating the delicate chemical balance between health and disease in the human body. As scientists unravel the base sequences of DNA, they obtain a greater appreciation for the roles that proteins play in the chemistry of life. Already the genes responsible for hemophilia, DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL Duchenne muscular dystrophy, and Huntington’s disease have been located. Once scientists have isolated a disease-causing gene, they can determine the protein that the gene has directed the cell to manufacture. By studying these proteins—or the absence of them—scientists will be able to devise a treatment for genetic disorders. A 13-year project to determine the order of bases on all 23 pairs of human chromosomes (also called the human genome) is now complete. Knowing where on a specific chromosome DNA codes for the production of a particular protein is useful for diagnosing and treating genetic diseases. This information is crucial for understanding the underlying causes of cancer. Also, comparing the human genome with that of other organisms will help us understand the role and implications of evolution. Replication of DNA Once the double-helix structure of DNA was discovered, how DNA duplicated itself before cell S division became apparent. The concept of base pairing in DNA suggests the analogy of positive and negative photographic film. Each strand of DNA in the double helix has the same informaM tion; one can make a positive print from a negative or a negative from a positive. 381 human genome The total DNA content found within the nucleus of a human cell; it is composed of approximately three billion base pairs of genetic information. replication The synthesis of new DNA from existing DNA. polymerase chain reaction (PCR) A technique for replicating or copying a portion of a DNA strand outside a living cell; this technique leads to millions of copies of the DNA strand. I The Process of Replication T The synthesis of new DNA from existing DNA begins with the unwinding of the DNA strands in the double helix. Each strand is then exposed to a collection of freeH nucleotides. Letter by letter, the double helix is re-created as the nucleotides are assembled in the ,proper order, as dictated by the ISBN: 978-1-323-16745-8 principle of base pairing (A with T and G with C). The result is the emergence of two identical copies of DNA where before there was only one (see Figure 15–4). A cell can now pass on its genetic identity when it divides. J Many enzymes and proteins are involved in unwinding the DNA strands, keeping the two O DNA strands apart, and assembling the new DNA strands. For example, DNA polymerases are enzymes that assemble a new DNA strand in the proper base sequence S determined by the original, or parent, DNA strand. DNA polymerases also “proofread” the growing DNA double helices H for mismatched base pairs, which are replaced with correct bases. Until recently, the phenomenon of DNA replication appeared U to be of only academic interest to forensic scientists interested in DNA for identification. However, A this changed when researchers perfected the technology of using DNA polymerases to copy a DNA strand located outside a living cell. This laboratory technique is known as polymerase chain reaction (PCR). Put simply, PCR is a technique 6 designed to copy or multiply DNA strands in a laboratory test tube. In PCR, small quantities of DNA or broken pieces of DNA8 found in crimescene evidence can be copied with the aid of a DNA polymerase. The copying 9 process is highly temperature dependent and can be accomplished in an automated fashion using a DNA thermal cycler (see Figure 15–5).0Each cycle of the PCR technique results in a doubling of the DNA, as shown in Figure 15–4. B Within a few hours, 30 cycles can multiply DNA a billionfold. Once DNA copies are in hand, they can be analyzed by any of the methods of modernUmolecular biology. The ability to multiply small bits of DNA opens new and exciting avenues for forensic scientists to explore. It means that sample size is no longer a limitation in characterizing DNA recovered from crime-scene evidence. Parent DNA unravels New double helices formed FIGURE 15–4 Replication of DNA. The strands of the original DNA molecule are separated, and two new strands are assembled. DNA Typing with Short Tandem Repeats Tandem Repeats Geneticists have discovered that portions of the DNA molecule contain sequences of letters that are repeated numerous times. In fact, more than 30 percent of the human genome is composed of repeating segments of DNA. These repeating sequences, or tandem repeats, seem to act as filler or spacers between the coding regions of DNA. Although these repeating segments do not seem tandem repeat A region of a chromosome that contains multiple copies of a core DNA sequence that are arranged in a repeating fashion. Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. 382 CHAPTER 15 inside the science Polymerase Chain Reaction The most important feature of PCR is the knowledge that an enzyme called DNA polymerase can be directed to synthesize a specific region of DNA. In a relatively straightforward manner, PCR can be used to repeatedly duplicate or amplify a strand of DNA millions of times. As an example, let’s consider a segment of DNA that we want to duplicate by PCR: –G–T–C–T–C–A–G–C–T–T–C–C–A–G– –C–A–G–A–G–T–C–G–A–A–G–G–T–C– To perform PCR on this DNA segment, short sequences of DNA on each side of the region of interest must be identified. In the example shown here, the short sequences are designated by boldface letters in the DNA segment. These short DNA segments must be available in a pure form known as a primer if the PCR technique is going to work. The first step in PCR is to heat the DNA strands to about 94°C. At this temperature, the double-stranded DNA molecules separate completely: –G–T–C–T–C–A–G–C–T–T–C–C–A–G– The second step is to add the primers to the separated strands and allow the primers to combine, or hybridize, with the strands by lowering the test-tube temperature to about 60°C. S M I T H , –G–T–C–T–C–A–G–C–T–T–C–C–A–G– J –C–A–G–A O C–C–A–G S –C–A–G–A–G–T–C–G–A–A–G–G–T–C– H The third step is to add the DNA polymerase and Ua mixture of free nucleotides (A, C, G, T) to the sepaArated strands. When the test tube is heated to 72°C, the polymerase enzyme directs the rebuilding of a double-stranded DNA molecule, extending the prim6ers by adding the appropriate bases, one at a time, resulting in the production of two complete pairs of 8double-stranded DNA segments: 9 0 B U –G–T–C–T–C–A–G–C–T–T–C–C–A–G– C–A–G–A–G–T–C–G–A–A–G–G–T–C– G–T–C–T–C–A–G–C–T–T–C–C–A–G –C–A–G–A–G–T–C–G–A–A–G–G–T–C– This completes the first cycle of the PCR technique, which results in a doubling of the number of DNA molecules from one to two. The cycle of heating, cooling, and strand rebuilding is then repeated, resulting in a further doubling of the DNA molecules. On completion of the second cycle, four double-stranded DNA molecules have been created from the original double-stranded DNA sample. Typically, 28 to 32 cycles are carried out to yield more than one billion copies of the original DNA molecule. Each cycle takes less than two minutes. Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. ISBN: 978-1-323-16745-8 –C–A–G–A–G–T–C–G–A–A–G–G–T–C– Copyright © 2012 Life Technologies Corporation. Used under permission FIGURE 15–5 The DNA Thermal Cycler, an instrument that automates the rapid and precise temperature changes required to copy a DNA strand. Within a matter of hours, DNA can be multiplied a millionfold. DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL 383 primer G–C–T G–G–T G–C–T G–G–C C–T–C Fifteen–base core FIGURE 15–6 A DNA segment consisting of a series of repeating DNA units. In this illustration, the 15-base core can repeat itself hundreds of times. The entire DNA segment is typically hundreds to thousands of bases long. A short strand of DNA used to target a region of DNA for replication by PCR. hybridization The process of joining two complementary strands of DNA to form a double-stranded molecule. WEBEXTRA 15.2 Polymerase Chain Reaction to affect our outward appearance or control any other basic genetic function, they are nevertheless part of our genetic makeup, inherited from our parents in the manner illustrated by the Punnett square (page 366). The origin and significance of these tandem repeats is a mystery, but to forensic scientists they offer a means of distinguishing one individual from another through DNA typing. Forensic scientists first began applying DNA technology toS human identity in 1985. From the beginning, attention has focused on the tandem repeats of the genome. These repeats can be Msame core sequence of DNA visualized as a string of connected boxes with each box having the bases (see Figure 15–6). All humans have the same type of repeats, I but there is tremendous variation in the number of repeats that each of us has. Up until the mid-1990s, the forensic community aimed its T efforts at characterizing repeat segments known as restriction fragment length polymorphisms H (RFLPs). A number of different RFLPs were selected by the forensic science community for performing DNA typing. , up to one thousand times. Typically a core sequence is 15 to 35 bases long and repeats itself These repeats are cut out of the DNA double helix by a restriction enzyme that acts like a pair of scissors. Once the DNA molecules have been cut up by the restriction enzyme, the resulting J known as electrophoresis. fragments were sorted out by separating the fragments by a technique RFLP DNA typing has the distinction of being the first scientifically O accepted protocol in the United States used for the forensic characterization of DNA. However, its utility has been short S In its short history, perhaps lived. New technology incorporating PCR has supplanted RFLP. RFLP’s most startling impact related to the impeachment trial H of President Bill Clinton. The whole complexion of the investigation regarding the relationship of the president with a White U House intern, Monica Lewinsky, changed when it was revealed that Ms. Lewinsky possessed a dress that she claimed was stained with the president’s semen. The AFBI Laboratory was asked to compare the DNA extracted from the dress stain with that of the president. An RFLP match was obtained between the president’s DNA and the stain. The combined frequency of occurrence for the seven DNA types found was nearly one in eight trillion, an undeniable link. The dress and a 6 copy of the FBI DNA report are shown in Figure 15–7. 8 Why couldn’t the PCR technology be applied to RFLP DNA typing? Simply put, the RFLP 9 used with DNA strands that strands are too long, often containing thousands of bases. PCR is best are no longer than a couple of hundred bases. The obvious solution to this problem is to charac0 terize DNA strands that are much shorter than RFLPs. Another advantage in moving to shorter DNA strands is that they would be expected to be more stable B and less subject to degradation brought about by adverse environmental conditions. The long RFLP strands tend to break apart U under adverse conditions not uncommon at crime scenes. ISBN: 978-1-323-16745-8 Short Tandem Repeats (STRs) Currently, short tandem repeat (STR) analysis has emerged as the most successful and widely used DNA-profiling procedure. STRs are locations (loci) on the chromosome that contain short sequence elements that repeat themselves within the DNA molecule. They serve as helpful markers for identification because they are found in great abundance throughout the human genome. STRs normally consist of repeating sequences of three to seven bases; the entire strand of an STR is also very short, less than 450 bases long. These strands are significantly shorter than those encountered in other DNA typing procedures. This means that STRs are much less susceptible to degradation and are often recovered from bodies or stains that have been subject to extreme decomposition. Also, because of their shortness, STRs are an ideal candidate for multiplication by PCR, thus overcoming the limited-sample-size problem often associated with crime-scene restriction fragment length polymorphisms (RFLPs) Different fragment lengths of base pairs that result from cutting a DNA molecule with restriction enzymes. electrophoresis A technique for separating molecules through their migration on a support medium while under the influence of an electrical potential. WEBEXTRA 15.3 An Animated Demonstration of Gel Electrophoresis short tandem repeat (STR) A region of a DNA molecule that contains short segments consisting of three to seven repeating base pairs. Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. 6 8 9 0 FIGURE 15–7 B The dress and the FBI Report of Examination for a semen stain located U on the dress. Q3243 Courtesy of Federal Bureau of Investigation J O S H U A Courtesy of Federal Bureau of Investigation S M I T H , Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. ISBN: 978-1-323-16745-8 384 inside the science Electrophoresis Electrophoresis is somewhat related to thin-layer chromatography (discussed in Chapter 9) in that it separates materials according to their migration rates on a stationary solid phase. However, electrophoresis does not use a moving liquid phase to move the material; instead, an electrical potential is placed across the stationary medium. The nature of the medium can vary; most forensic applications call for a starch or agar gel coated onto a glass plate. Under these conditions, only substances that possess an electrical charge migrate across the stationary phase (see Figure 1 [a–c]). Because many substances in blood carry an electrical charge, they Power source Mixtures of DNA fragments of different sizes placed on gel-coated plate can be separated and identified by electrophoresis. The technique is particularly useful for separating and identifying complex biochemical mixtures. In forensic science, electrophoresis is most useful for characterizing proteins and DNA in dried blood. Forensic serologists have developed several electrophoretic procedures for characterizing DNA in dried blood. Mixtures of DNA fragments can be separated by gel electrophoresis by taking advantage of the fact that the rate of movement of DNA across a gel-coated plate depends on the molecule’s size. Smaller DNA fragments move faster along the plate than larger DNA fragments. After completing the electrophoresis run, the separated DNA is stained with a suitable developing agent for visual observation (see Figure 2). S M Power source I T H , Electric potential applied to plate Substances with an electrical charge migrate across plate Gel-coated plate (a) J O S Separated bands allow analyst to characterize H DNA in dried blood U A (b) Power source Longer fragments move more slowly Shorter fragments move more quickly 6 Completed gel 8 FIGURE 1 9 The technique of gel electrophoresis. (a) Applying samples to the plate. (b) Applying electric potential to 0 of the fragments on the gel allows for analysis. the plate to cause the fragments to migrate. (c) Separation B FIGURE 2 DNA fragments separated U (c) Explorer/Science Source ISBN: 978-1-323-16745-8 by gel electrophoresis are visualized under a UV light. 385 Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. 386 CHAPTER 15 A A T – G A AA T G T G T G – AA A A G AT – A T G Dorling Kindersley Limited – A AA T G G A A T G – T A – – T G AA G AT – A A – T G – T G AA – – S M I– A A T G AA T FIGURE 15–8 Variants of the short tandemH repeat TH01. The upper DNA strand contains six repeats of the sequence A-A-T-G; the lower DNA strand contains eight repeats of the , sequence A-A-T-G. This DNA type is designated as TH01 6,8. J 18 DNA-containing cells is needed to obtain a DNA profile. evidence. Only the equivalent of For instance, STR profiles haveO been used to identify the origin of saliva residue on envelopes, stamps, soda cans, and cigarette butts. To understand the utility ofS STRs in forensic science, let’s look at one commonly used STR known as TH01. This DNA segment H contains the repeating sequence A–A–T–G. Seven TH01 variants have been identified in the human genome. These variants contain 5 to 11 repeats of U A–A–T–G. Figure 15–8 illustrates two such TH01 variants, one containing 6 repeats and the other containing 8 repeats of A–A–T–G. A During a forensic examination, TH01 is extracted from biological materials and amplified by PCR as described earlier. The ability to copy an STR means that extremely small amounts of the molecule can be detected and 6 analyzed. Once the STRs have been copied or amplified, they are separated by electrophoresis. Here, the STRs are forced to move across a gel-coated plate 8 under the influence of an electrical potential. Smaller DNA fragments move along the plate faster than do larger DNA fragments.9 By examining the distance the STR has migrated on the electrophoretic plate, one can determine the number of A–A–T–G repeats in the STR. Every person has 0 two STR types for TH01, one inherited from each parent. Thus, for example, one may find in a B and eight repeats. This combination of TH01 is found in apsemen stain TH01 with six repeats proximately 3.5 percent of the population. It is important to understand that all humans have the U same type of repeats, but there is tremendous variation in the number of repeats each of us has. When examining an STR DNA pattern, one merely needs to look for a match between band sets. For example, in Figure 15–9 DNA extracted from a crime-scene stain matches the DNA recovered from one of three suspects. When comparing only one STR, a limited number of people in a population would have the same STR fragment pattern as the suspect. However, by using additional STRs, a high degree of discrimination or complete individualization can be achieved. multiplexing A technique that simultaneously detects more than one DNA marker in a single analysis. What makes STRs so attractive to forensic scientists is that hundreds of types of STRs are found in human genes. The more STRs one can characterize, the smaller the percentage of the population from which these STRs can emanate. This gives rise to the concept of multiplexing. Using PCR technology, one can simultaneously extract and amplify a combination of different STRs. Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. ISBN: 978-1-323-16745-8 Multiplexing DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL 387 FIGURE 15–9 A DNA profile pattern of a suspect and its match to crime-scene DNA. From left to right, lane 1 is a DNA standard marker; lane 2 is the crimescene DNA; and lanes 3 to 5 are control samples from suspects 1, 2, and 3, respectively. Crimescene DNA matches suspect #2. S M I T H , This kit provides One STR system on the commercial market is the STR Blue Kit. ISBN: 978-1-323-16745-8 8 DNA Typing with STRs 9 The 13 CODIS STRs are listed in Table 15–1 along with their 0 probabilities of identity. The probability of identity is a measure of the likelihood that two individuals selected at random will have an identical STR type. TheBsmaller the value of this probability, the more discriminating the STR. A high degree U of discrimination and even individualization can be attained by analyzing a combination of STRs (multiplexing). Because STRs occur independently of each other, the probability of biological evidence having a particular combination of STR types is determined by the product of their frequency of occurrence in a population. This combination is referred to as the product rule (see page 64). Hence, the greater the number of STRs characterized, the smaller the frequency of occurrence of the analyzed sample in the general population. The combination of the first 3 STRs shown in Table 15–1 typically produces a frequency of occurrence of about 1 in 5,000. A combination of the first 6 STRs typically yields a frequency of occurrence in the range of one in two million for the Caucasian population, and if the top 9 STRs are determined in combination, this frequency declines to about one in one billion. The combination of all 13 STRs shown in Table 15–1 typically produces frequencies of occurrence that measure in the Questioned stain Control stain FGA vWA Size Markers the necessary materials for amplifying and detecting three STRs (a process called triplexing): D3S1358, vWA, and FGA. The design of the system ensures that the size J clearly on an of the STRs does not overlap, thereby allowing each marker to be viewed electrophoretic gel, as shown in Figure 15–10. In the United States, O the forensic science community has standardized 13 STRs for entry into a national database known as the S Combined DNA Index System (CODIS). When an STR is selected for analysis, not only must the identity H and number of core repeats be defined, but the sequence of bases flanking the repeats must U also be known. This knowledge allows commercial manufacturers of STR typing kits to prepare the correct primers to delineate the STR segment A to be amplified by PCR. Also, a mix of different primers aimed at different STRs will be used to simultaneously amplify a multitude of STRs (i.e., to multiplex). In fact, one STR kit on the commercial market can simultaneously make copies of615 different STRs (see Figure 15–11). D3S1358 FIGURE 15–10 A triplex system containing three loci: FGA, vWA, and D3S1358, indicating a match between the questioned and the standard/reference stains. Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. CHAPTER 15 FIGURE 15–11 STR profile for 15 loci. S M I T H , Richard Saferstein 388 J O TABLE 15–1 S Probability of Identities The 13 CODIS STRs and Their HAfrican American STR U D3S1358 0.094 A vWA 0.063 FGA TH01 TPOX CSF1PO D5S818 D13S317 D7S820 D8S1179 D21S11 D18S51 D16S539 6 8 9 0 B U 0.033 0.109 0.090 0.081 0.112 0.136 0.080 0.082 0.034 0.029 0.070 U.S. Caucasian 0.075 0.062 0.036 0.081 0.195 0.112 0.158 0.085 0.065 0.067 0.039 0.028 0.089 Source: The Future of Forensic DNA Testing: Predictions of the Research and Development Working Group. Washington, D.C.: National Institute of Justice, Department of Justice, 2000, p. 41. WEBEXTRA 15.4 range of 1 in 575 trillion for Caucasian Americans and 1 in 900 trillion for African Americans. Importantly, several commercially available kits allow forensic scientists to profile STRs in the kinds of combinations cited here. Sex Identification Using STRs amelogenin gene A genetic locus useful for determining gender. Manufacturers of commercial STR kits typically used by crime laboratories provide one additional piece of useful information along with STR types: the sex of the DNA contributor. The focus of attention here is the amelogenin gene located on both the X and Y chromosomes. This Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. ISBN: 978-1-323-16745-8 Understand the Operational Principles of Capillary Electrophoresis DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL gene, which is actually the gene for tooth pulp, has an interesting characteristic in that it is shorter by six bases in the X chromosome than in the Y chromosome. Hence, when the amelogenin gene is amplified by PCR and separated by electrophoresis, males, who have an X and a Y chromosome, show two bands; females, who have two X chromosomes, have just one band. Typically, these results are obtained in conjunction with STR types. Another tool in the arsenal of the DNA analyst is the ability to type STRs located on the Y chromosome. The Y chromosome is male specific and is always paired with the X chromosome. Although more than 400 Y-STRs have been identified, only a small number of them are being used for forensic applications. One commercial kit allows for the characterization of 17 Y chromosome STRs. When can it be advantageous to seek out Y-STR types? Generally, Y-STRs are useful for analyzing blood, saliva, or a vaginal swab that is a mix originating from more than one male. For example, Y-STRs prove useful when multiple males are involved in a sexual assault. Further simplifying the analysis is that any DNA in the mixture that originates from a female will not show. Keep in mind that STR types derived from the Y chromosome originate only from this single male chromosome. A female subject, or one with an XXS chromosome pattern, does not contribute any DNA information. Also, unlike a conventional STR type that is derived from two chromosomes and typically shows two bands or peaks, a Y-STRM has only one band or peak for each STR type. I For example, the traditional STR DNA pattern may prove to be overly complex in the case T would be expected to show of a vaginal swab containing the semen of two males. Each STR type four bands, two from each male. Also complicating the appearance H of the DNA profile may be the presence of DNA from skin cells emanating from the walls of the vagina. In this circum, stance, homing in on the Y chromosome greatly simplifies the appearance and interpretation of the DNA profile. Thus, when presented with a DNA mixture of two males and one female, Y-STR analysis would show only two bands (one band for each male) for each Y-STR type. J When gauging the significance of a Y-STR match between questioned and known specimens, one should take into consideration that all male paternal O relatives (e.g., brothers, father, male offspring, and uncles) would be expected to have the same Y-STR profile. S Another advantage of employing STR technology is to extend the success of detecting evidenH experience has demonstrated tial DNA from vaginal swabs collected from rape victims. Casework significant difficulties in obtaining traditional STR DNA profiles for the male donor from vaginal U swabs collected after three to four days after intercourse. However, the application of Y-STR techA for the male donor. nology often extends the routine postcoital detection time to five days 389 Y-STRs Short tandem repeats located on the human Y chromosome. 6 8 9 0 B high-voltage energy. The column is coated with a gel U polymer, and the DNA-containing sample solution is inside the science ISBN: 978-1-323-16745-8 Capillary Electrophoresis The separation of STRs can typically be carried out on a flat gel-coated electrophoretic plate, as described earlier. However, the need to reduce analysis time and to automate sampling and data collection has led to the emergence of capillary electrophoresis as the preferred technology for characterization of STRs. Capillary electrophoresis is carried out in a thin glass column rather than on the surface of a coated-glass plate. As illustrated in the figure, each end of the column is immersed in a reservoir of buffer liquid that also holds electrodes (coated with platinum) to supply injected into one end of the column by applying a high voltage to an electrode immersed in the DNA solution. The STR fragments then move through the column under the influence of an electrical potential at a speed that is related to the length of the STR fragments. The other end of the column is connected to a detector that tracks the separated STRs as they emerge from the column. As the DNA peaks pass through the detector, they are recorded on a display known as an electropherogram, as shown in the figure. (continued ) Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. 390 CHAPTER 15 Electrical potential is applied to STR fragments in column Voltage supply Fragments move at different speeds through column under influence of electric potential Sample containing DNA is injected into capillary column Capillary column Injection Area S M Detector I Platinum-coated T electrodes H , (a) J O S H Detector tracks separated STRs Ucolumn as they emerge from A Voltage supply Injection Area Capillary column 6 8 9 0 Detector B U Electropherogram recorder shows separation pattern of STRs (b) Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. ISBN: 978-1-323-16745-8 Capillary electrophoresis technology has evolved from the traditional flat gel electrophoresis approach. The separation of DNA segments is carried out on the interior wall of a glass capillary tube that is kept at a constant voltage. The size of the DNA fragments determines the speed at which they move through the column. This figure illustrates the separation of three sets of STRs (triplexing). DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL 391 inside the science MiniSTRs The forensic science community turned to STRs when it became apparent that short segments of DNA would be required to meet the requirements of PCR. Commercial manufacturers of DNA-typing kits prepared a series of 13 STRs for compatibility with the CODIS DNA database that ranged in length from 100 to 450 bases. One obvious benefit in working with short DNA segments was the likelihood that useful information could be extracted even from fragmented DNA. This often proved to be the case, but not always. On occasion, degraded DNA is encountered that is so badly damaged that traditional STR analysis is not possible. Prolonged exposure of DNA to extreme environmental elements, such as temperature extremes, humidity, or microbial activity, can lead to such degradation. An approach to dealing with this problem is to further shorten the STR strands that emerge from the PCR process. The approach that has been taken to accomplish this task is to create new primers that can be positioned closer to the STR repeat region (see the figure). The shorter STR products (called amplicons) that now emerge from PCR increase the chances of C C A G G G T C Primer G G T characterizing badly fragmented strands of DNA. These smaller amplicons are called “miniSTRs.” One manufacturer of STR kits has produced a miniSTR kit designed to amplify eight miniSTRs, seven of which are totally compatible with the CODIS database. The miniSTRs range in size from 71 to 250 bases. A DNA analyst suspecting a degraded sample now has the option, if sample size permits, of running both traditional STR and miniSTR determinations, or just the latter. The advent of miniSTRs means that forensic scientists can now analyze samples that were once S thought to be of no value. One of the first benefacM tors of miniSTR technology was the identification of a number of victims from the Waco Branch Davidian I fire. Also, a number of World Trade Center victims T were identified by miniSTR technology. Another focus of attention has been human hair. In the past, exH tracting nuclear DNA out of the hair shaft has been , enormously difficult; the number of STRs in hair has been found to be very low as well as highly degraded. However, one study has demonstrated that miniSTRs J may overcome some of the difficulties in obtaining partial profiles from the degraded DNA present in O shed hair.2 S H U A A T A T T C T C Primer ISBN: 978-1-323-16745-8 A A G T 6 Appropriate primers are positioned close to the repeat 8 units of a DNA segment in order to initiate the PCR process that will create short or mini STRs. 9 0 B WEBEXTRA 15.5 Significance of DNA Typing U See the 13 CODIS STRs and Their C STR DNA typing has become an essential and basic investigative tool in the law enforcement community. The technology has progressed at a rapid rate and in only a few years has surmounted numerous legal challenges to become vital evidence for resolving violent crimes and sex offenses. DNA evidence is impartial, implicating the guilty and exonerating the innocent. In a number of well-publicized cases, DNA evidence has exonerated individuals who have been wrongly convicted and imprisoned. The importance of DNA analyses in criminal investigations has also placed added burdens on crime laboratories to improve their quality-assurance procedures and to ensure the correctness of their results. In several well-publicized instances, the accuracy of DNA tests conducted by government-funded laboratories has been called into question. 2 Chromosomal Positions WEBEXTRA 15.6 See How to Calculate the Frequency of Occurrence of a DNA Profile WEBEXTRA 15.7 See the Electropherogram Record from One Individual’s DNA WEBEXTRA 15.8 An Animation Depicting Y-STRs K. E. Opel et al., “Evaluation and Quantification of Nuclear DNA from Human Telogen Hairs,” Journal of Forensic Sciences 53 (2008): 853. Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. 392 CHAPTER 15 The Combined DNA Index System (CODIS) Perhaps the most significant investigative tool to arise from a DNA-typing program is CODIS (Combined DNA Index System), a computer software program developed by the FBI that maintains local, state, and national databases of DNA profiles from convicted offenders, unsolved crime-scene evidence, and profiles of missing people. CODIS allows crime laboratories to compare DNA types recovered from crime-scene evidence to those of convicted sex offenders and other convicted criminals. Thousands of CODIS matches have linked serial crimes to each other and have solved crimes by allowing investigators to match crime-scene evidence to known convicted offenders. This capability is of tremendous value to investigators in cases in which the police have not been able to identify a suspect. The CODIS concept has already had a significant impact on police investigations in various states, as shown in the Case Files feature on page 70. S Mitochondrial DNA M mitochondria case files Small structures located outside the nucleus of a cell; these structures supply energy to the cell; maternally inherited DNA is found in each mitochondrion. Typically, when one describes IDNA in the context of a criminal investigation, the subject is assumed to be the DNA in the nucleus of a cell. Actually, a human cell contains two types of T The first constitutes the 23 pairs of chromosomes in the nuclei DNA—nuclear and mitochondrial. of our cells. Each parent contributes H to the genetic makeup of these chromosomes. Mitochondrial DNA (mtDNA), on the other hand, is found outside the nucleus of the cell and is inherited solely , from the mother. Mitochondria are cell structures found in all human cells. They are the power plants of the body, providing about 90 percent of the energy that the body needs to function. A single mitochondrion contains severalJloops of DNA, all of which are involved in energy generation. Further, because each cell in our Obodies contains hundreds to thousands of mitochondria, there are hundreds to thousands of mtDNA copies in a human cell. This compares to just one set of Cold Case Hit S H U A 6 In 1990, a series of attacks on elderly victims was committed in8 Goldsboro, North Carolina, by an unknown individual dubbed 9 the Night Stalker. During one such attack in March, an elderly woman was brutally sexually assaulted and almost murdered.0 Her daughter’s early arrival home saved the woman’s life. The suspect fled, leaving behind materials intended to burn the resi-B dence and the victim in an attempt to conceal the crime. U In July 1990, another elderly woman was sexually as- Source: National Institute of Justice, “Using DNA to Solve Cold Cases” (NIJ Special Report), July 2002. Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. ISBN: 978-1-323-16745-8 saulted and murdered in her home. Three months later, a third elderly woman was sexually assaulted and stabbed to death. Her husband was also murdered. Although their house was set alight in an attempt to cover up the crime, fire and rescue personnel pulled the bodies from the house before it was engulfed in flames. DNA analysis of biological evidence collected from vaginal swabs from the three sexual assault victims enabled authorities to conclude that the same perpetrator had committed all three crimes. However, there was no suspect. More than ten years after these crimes were committed, law enforcement authorities retested the biological evidence from all three cases using newer DNA technology and entered the DNA profiles into North Carolina’s DNA database. The DNA profile developed from the crime-scene evidence was compared to thousands of convicted-offender profiles already in the database. In April 2001, a “cold hit” was made: The DNA profiles was matched to that of an individual in the convicted-offender DNA database. The perpetrator had been convicted of shooting into an occupied dwelling, an offense that requires inclusion of the convict’s DNA in the North Carolina DNA database. The suspect was brought into custody for questioning and was served with a search warrant to obtain a sample of his blood. That sample was analyzed and compared to the crime-scene evidence, confirming the DNA database match. When confronted with the DNA evidence, the suspect confessed to all three crimes. DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL 393 inside the science Familial DNA—Expanding the DNA Database In 1984, Deborah Sykes was raped and stabbed to death as she walked to work in Winston-Salem, North Carolina. A month later, Darryl Hunt, then 19 years old, was arrested and eventually convicted of the crime. Hunt insisted that he was innocent, and by 1990, DNA testing of semen found on Sykes proved that he was not its source. Nevertheless, North Carolina prosecutors ignored this new evidence and he remained in jail. Finally, a search against Darryl Hunt’s STR profile in the North Carolina DNA database revealed a close but not perfect match to a genetic profile already in the database, that of his brother. Upon further investigation, that man, Willard Brown, confessed to Sykes’s murder in 2003, and Hunt was finally freed from prison. In this case, DNA profiling exonerated an innocent man and helped lead the police to the real culprit. The Sykes case illustrates how the contents of a criminal DNA database can be dramatically expanded to aid the police in identifying criminals by searching the database for near matches. Typically, the CODIS database is used to find exact matches with crime-scene DNA. However, taking into account the facts that the 13 STR loci that constitute U.S. offender DNA databases are genetically inherited and that each individual’s DNA profile is genetically determined by one’s parents creates opportunities to use the database’s raw data to search out close relatives. DNA profiles of related individuals are likely to show a higher proportion of shared STR loci as compared to unrelated individuals. Hence, searching the database for profiles that have a high degree of commonality may lead to the identification of a close relative of the perpetrator. Interestingly, studies have shown that a person’s chances of committing a crime increase if a parent or sibling had previously done so. A 1999 U.S. Department of Justice survey found that 46 percent of jail inmates had at least one close relative who had also been incarcerated. The potential for improving the effectiveness of DNA database searches is considerable. Familial searches of a DNA database would dramatically increase the size of the database by three or more times S because every profile that is entered would, in effect, contain genetic information about the STR alleles of M the donor’s parents, siblings, and children. One study I estimates that using familial DNA searches could increase the “cold hit” rates by 40 percent. Considering T the fact that there have been about 95,000 cold hits in H the United States, familial DNA has the potential for identifying thousands of additional criminal suspects. , The concept of familial DNA searching has been routinely adopted in the United Kingdom. In the United States, the FBI notifies investigators about J close matches it finds using its current software, but O the agency has no current plans to modify its search algorithms to optimize the database’s capacity to ferS ret out near or close matches. This leaves it up to the H states to decide whether to release identifying inforabout an offender whose DNA closely matches U mation a crime-scene sample from another state. Challengers A to familial database searching have cited it as a violation of constitutional protections against unreasonable search and seizure. A number of mixed state court de6 cisions have failed to produce a consensus on the constitutionality of familial DNA database searches. ISBN: 978-1-323-16745-8 8 9 0 B nuclear DNA located in that same cell. Thus, forensic scientists are offered enhanced sensitivity and the opportunity to characterize mtDNA when nuclear DNAU is significantly degraded, such as in charred remains, or when nuclear DNA may be present in a small quantity (such as in a hair shaft). Interestingly, when authorities cannot obtain a reference sample from an individual who may be long deceased or missing, an mtDNA reference sample can be obtained from any maternally related relative. However, all individuals of the same maternal lineage will be indistinguishable by mtDNA analysis. Although mtDNA analysis is significantly more sensitive than nuclear DNA profiling, forensic analysis of mtDNA is more rigorous, time consuming, and costly than nuclear DNA profiling. For this reason, only a handful of public and private forensic laboratories receive evidence for this type of determination. The FBI Laboratory has imposed strict limitations on the types of cases in which it will apply mtDNA technology. sequencing A procedure used to determine the order of the base pairs that constitute DNA. Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. 394 CHAPTER 15 inside the science Forensic Aspects of Mitochondrial DNA As was previously discussed, nuclear DNA is composed of a continuous linear strand of nucleotides (A, T, G, and C). On the other hand, mtDNA is constructed in a circular or loop configuration. Each loop contains enough A, T, G, and C (approximately 16,569 units) to make up 37 genes involved in mitochondrial energy generation. Two regions of mtDNA have been found to be highly variable in the human population. These two regions have been designated hypervariable region I (HV1) and hypervariable region II (HV2), as shown in the figure. As indicated previously, the process for analyzing HV1 and HV2 is tedious. It involves generating many copies of these DNA hypervariable regions by PCR and then determining the order of the A–T–G–C bases constituting the hypervariable regions. This process is known as sequencing. The FBI Laboratory, the Armed Forces DNA Identification O S H U Mitochondria A CELL Nucleus Control Region HV1 Laboratory, and other laboratories have collaborated to compile an mtDNA population database containing the base sequences from HV1 and HV2. Once the sequences of the hypervariable regions from a case sample are obtained, most laboratories simply report the number of times these sequences appear in the mtDNA database maintained by the FBI. The mtDNA database contains about five thousand sequences. This approach permits an assessment of Show common or rare an observed mtDNA sequence is in the database. Interestingly, many of the sequences Mthat have been determined in casework are unique I to the existing database, and many types are present at frequencies no greater than 1 percent in the dataTbase. Thus it is often possible to demonstrate how unHcommon a particular mitochondrial DNA sequence is. However, even under the best circumstances, mtDNA , typing does not approach STR analysis in its discrimination power. Thus, mtDNA analysis is best reserved for samples for which nuclear DNA typing is simply Jnot possible. HV2 6 8 9 0 B U Mitochondrial DNA Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. ISBN: 978-1-323-16745-8 Every cell in the body contains hundreds of mitochondria, which provide energy to the cell. Each mitochondrion contains numerous copies of DNA shaped in the form of a loop. Distinctive differences between individuals in their mitochondrial DNA makeup are found in two specific segments of the control region on the DNA loop known as HV1 and HV2. DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL Collection and Preservation of Biological Evidence for DNA Analysis WEBEXTRA 15.9 Since the early 1990s, the advent of DNA profiling has vaulted biological crime-scene evidence to a stature of importance that is eclipsed only by the fingerprint. In fact, the high sensitivity of DNA determinations has even changed the way police investigators define biological evidence. Just how sensitive is STR profiling? Forensic analysts using currently accepted protocols can reach sensitivity levels as low as 125 picograms. Interestingly, a human cell has an estimated 7 picograms of DNA, which means that only 18 DNA-bearing cells are needed to obtain an STR profile. However, modifications in the technology can readily extend the level of detection down to 9 cells. A quantity of DNA that is below the normal level of detection is defined as a low copy number. (However, analysts must take extraordinary care in analyzing low-copy-number DNA and often may find that courts will not allow this data to be admissible in a criminal trial.) With this technology in hand, the horizon of the criminal investigator extends beyond the traditional S with saliva, a cup or can that dried blood or semen stain to include stamps and envelopes licked has touched a person’s lips, chewing gum, the sweat band of a hat, Mor a bedsheet containing dead skin cells. Likewise, skin or epithelial cells transferred onto the surface of a weapon, the interior I of a glove, or a pen have yielded DNA results.3 The phenomenon of transferring DNA via skin cells onto theTsurface of an object has come to be called touch DNA. Again, keep in mind that, in theory, only 18 skin cells deposited on an H object are required to obtain a DNA profile. WEBEXTRA 15.10 , Collection of Biological Evidence However, before investigators become enamored with the wonders of DNA, they should first J realize that the crime scene must be treated in the traditional manner. Before the collection of Oup and its location relative to evidence begins, biological evidence should be photographed close the entire crime scene recorded through notes, sketches, and photographs. If the shape and posiS tion of bloodstains may provide information about the circumstances of the crime, an expert must H The significance of the immediately conduct an on-the-spot evaluation of the blood evidence. position and shape of bloodstains can best be ascertained when theUexpert has an on-site overview of the entire crime scene and can better reconstruct the movement of the individuals involved. A phase of the investigation is No attempt should be made to disturb the blood pattern before this completed. The evidence collector must handle all body fluids and biologically stained materials with a 6 minimum amount of personal contact. All body fluids must be assumed to be infectious; hence, wearing disposable latex gloves while handling the evidence is required. Latex gloves also sig8 nificantly reduce the possibility that the evidence collector will contaminate the evidence. These 9 phase of the investigation. gloves should be changed frequently during the evidence-collection Safety considerations and avoidance of contamination also call 0 for the wearing of face masks, a lab coat, eye protection, shoe covers, and possibly coveralls. The deposition of DNA onto crime-scene objects via saliva,B sweat, skin, blood, and semen has created a vast array of forensic evidence that is quite different Ufrom the traditional evidence collected at crime scenes prior to the DNA era (see Table 15–2). 395 See How We Inherit Our Mitochondrial DNA Look into the Structure of Mitochondrial DNA and See How It Is Used for DNA Typing picogram One-trillionth of a gram, or 0.000000000001 gram. low copy number Fewer than 18 DNA-bearing cells. epithelial cells The outer layer of skin cells; these DNA-bearing cells often fall off or are rubbed off onto objects retrieved from crime scenes. touch DNA DNA from skin cells transferred onto the surface of an object by simple contact. ISBN: 978-1-323-16745-8 Packaging of Biological Evidence Biological evidence should not be packaged in plastic or airtight containers because accumulation of residual moisture could contribute to the growth of DNA-destroying bacteria and fungi. Each stained article should be packaged separately in a paper bag or a well-ventilated box. A red-bio-hazard label must be attached to each container. If feasible, the entire stained article 3 R. A. Wickenheiser, “Trace DNA: A Review, Discussion of Theory, and Application of the Transfer of Trace Qualities through Skin Contact,” Journal of Forensic Sciences 47 (2002): 442. Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. 396 CHAPTER 15 TABLE 15–2 Location and Sources of DNA at Crime Scenes substrate control Possible Location of DNA on the Evidence Baseball bat or similar weapon Hat, bandanna, mask Eyeglasses Facial tissue, cotton swab Handle, end Inside Nose or ear pieces, lens Surface area Dirty laundry Toothpick Used cigarette Stamp or envelope Tape or ligature Bottle, can, glass Used condom Surface area Tips Cigarette butt Licked area Inside/outside surface Sides, mouthpiece Inside/outside surface S M I Blanket, pillow, sheet T “Through and through” bullet H Bite mark Fingernail, partial fingernail , buccal cells Cells derived from the inner cheek lining. Outside surface Person’s skin or clothing Scrapings Sweat, skin, blood, tissue Sweat, hair, dandruff Sweat, skin Mucus, blood, sweat, semen, ear wax Blood, sweat, semen Saliva Saliva Saliva Skin, sweat Saliva, sweat Semen, vaginal or rectal cells Sweat, hair, semen, urine, saliva Blood, tissue Saliva Blood, sweat, tissue J O and submitted for examination. If this is not possible, dried should be packaged blood is best S removed from a surface with a sterile cotton-tipped swab lightly moistened with distilled water from a dropper bottle. A portion of the unstained H near the recovered stain must likewise be removed or swabbed surface material and placed inUa separate package. This is known as a substrate control. The forensic examiner may use the substrate swab to confirm that the results of A were brought about by the stain and not by the material on the tests performed which it was deposited. However, this practice is normally not necessary when DNA determinations are carried out in the laboratory. One point is critical, and 6 collected swabs must not be packaged in a wet state. After the that is that the collection is 8 made, the swab must be air-dried for approximately five to ten minutes. Then it is best to place it in a swab box (see Figure 15–12), which has 9 to allow air circulation. The swab box can then be placed in a a circular hole paper or manila 0 envelope. All packages containing biological evidence should be refrigerated or B location out of direct sunlight until delivery to the laboratory. stored in a cool However, oneUcommon exception is blood mixed with soil. Microbes present in soil rapidly degrade DNA. Therefore, blood in soil must be stored in a clean glass or plastic container and immediately frozen. Obtaining DNA Reference Specimens Biological evidence attains its full forensic value only when an analyst can compare each of its DNA types to known DNA samples collected from victims and suspects. The least intrusive method for obtaining a DNA standard/reference, one that nonmedical personnel can readily use, is the buccal swab. Cotton swabs are placed in the subject’s mouth and the inside of the cheek is vigorously swabbed, resulting in the transfer of buccal cells onto the swab (see Figure 15–13). If an individual is not available to give a DNA standard/reference sample, some interesting alternatives are available to evidence collectors, including a toothbrush, combs and hairbrushes, Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. ISBN: 978-1-323-16745-8 FIGURE 15–12 Air-dried swabs are placed in a swab box for delivery to the forensic laboratory. Surface area Source of DNA Source: National Institute of Justice, U.S. Department of Justice. Courtesy of Tri-Tech Forensics, Inc., Southport, NC An unstained object adjacent to an area on which biological material has been deposited. Evidence DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL 397 a razor, soiled laundry, used cigarette butts, and earplugs. Any of these items may contain a sufficient quantity of DNA for typing purposes. Interestingly, as investigators worked to identify the remains of victims of the World Trade Center attack on September 11, 2001, the families of the missing were requested to supply the New York City DNA Laboratory with these types of items in an effort to match recovered DNA with human remains. S M I T H , ISBN: 978-1-323-16745-8 6 8 9 0 B U Courtesy of Tri-Tech Forensics, Inc., Southport, NC J O S H U A FIGURE 15–13 A buccal swab collection kit is designed for use by nonmedical personnel. The cotton-tipped swabs are placed in the subject’s mouth and the inside of the cheek is vigorously swabbed, resulting in the transferr of buccal cells onto the cotton bulb of the swab. The kit is then delivered to the forensic laboratory. Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. 398 CHAPTER 15 Contamination of DNA Evidence One key concern during the collection of a DNA-containing specimen is contamination. Contamination can occur by introducing foreign DNA through coughing or sneezing onto a stain during the collection process, or there can be a transfer of DNA when items of evidence are incorrectly placed in contact with each other during packaging. Fortunately, an examination of DNA band patterns in the laboratory readily reveals the presence of contamination. For example, with an STR, one will expect to see a two-band pattern. More than two bands suggest a mixture of DNA from more than one source. Crime-scene investigators can take some relatively simple steps to minimize contamination of biological evidence: 1. Use disposable gloves. 2. Wear a face mask while collecting evidence, a lab coat, eye protection, as well as shoe covers. 3. Change gloves before handling each new piece of evidence. 4. Collect a substrate control S for possible subsequent laboratory examination. 5. Pick up small items of evidence such as cigarette butts and stamps with clean forceps. DisM so that they can be discarded after a single evidence collection. posable forceps are to be used 6. Always package each itemIof evidence in its own well-ventilated container. WEBEXTRA 15.11 Step into the Role of the First Responding Officer at a Burglary Scene A common occurrence at crime T scenes is to suspect the presence of blood but not be able to observe any with the naked eye. In these situations, the common test of choice is luminol or H Bluestar (see page 363). Interestingly, neither luminol nor Bluestar is expected to inhibit the ability to detect and characterize , STRs.4 Therefore, luminol and Bluestar can be used to locate traces of blood and areas that have been washed nearly free of blood without compromising the potential for DNA typing. WEBEXTRA 15.12 case files Assume the Duties of an Evidence Collection Technician at a Burglary Scene J O S H Contact Lens Evidence U A woman alleged that she had been held against her will and sexually assaulted by a male friend in an apartment. During theA course of the assault, a contact lens was knocked from the victim’s eye. After the assault, she escaped, but because she was afraid of the threats made by her attacker, she did not report the6 assault to the police for three days. When the police examined the apartment, they noted that it had been thoroughly cleaned.8 A vacuum cleaner bag was seized for examination, and several STR Locus D3S1358 FGA vWA TH01 F13A1 fes/fps D5S818 D13S317 D7S820 9 0 15, 18 B 24, 25 17,U 17 pieces of material resembling fragments of a contact lens were discovered within the bag. In the laboratory, approximately 20 nanograms of human DNA was recovered from the contact lens fragments. Cells from both the eyeball and the interior of the eyelids are naturally replaced every 6 to 24 hours. Therefore, both are potential sources for the DNA found. The DNA profile originating from the fragments matched the victim, thus corroborating the victim’s account of the crime. The estimated population frequency of occurrence for the nine matching STRs are approximately 1 in 850 million. The suspect subsequently pleaded guilty to the offense. Victim’s DNA Type Contact Lens 6, 7 5, 6 11, 12 11, 12 11, 12 10, 12 15, 18 24, 25 17, 17 6, 7 5, 6 11, 12 11, 12 11, 12 10, 12 4 A. M. Gross et al., “The Effect of Luminol on Presumptive Tests and DNA Analysis Using the Polymerase Chain Reaction,” Journal of Forensic Sciences 44 (1999): 837. Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. ISBN: 978-1-323-16745-8 Based on information in R. A. Wickenheiser and R. M. Jobin, “Comparison of DNA Recovered from a Contact Lens Using PCR DNA Typing,” Canadian Society of Forensic Science Journal 32 (1999): 67. ISBN: 978-1-323-16745-8 case files DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL The JonBenét Ramsey Murder Case Point–Counterpoint Point July 9, 2008 Boulder District Attorney Mary T. Lacy issues the following announcement with regard to the investigation of the murder of JonBenét Ramsey. On December 25–26, 1996, JonBenét Ramsey was murdered in the home where she lived with her mother, father and S brother. Despite a long and intensive investigation, the death of JonBenét remains unsolved. M The murder has received unprecedented publicity and has been shrouded in controversy. That publicity has led to many I theories over the years in which suspicion has focused on one T family member or another. However, there has been at least one persistent stumbling block to the possibility of prosecuting H any Ramsey family members for the death of JonBenét—DNA. , As part of its investigation of the JonBenét Ramsey homicide, the Boulder Police identified genetic material with apparent evidentiary value. Over time, the police continued to investigate DNA, including taking advantage of advances in J the science and methodology. One of the results of their efforts O was that they identified genetic material and a DNA profile from drops of JonBenét’s blood located in the crotch of the unS derwear she was wearing at the time her body was discovered. That genetic profile belongs to a male and does not belong to H anyone in the Ramsey family. U The police department diligently compared that profile to a very large number of people associated with the victim, with A her family, and with the investigation, and has not identified the source, innocent or otherwise, of this DNA. The Boulder Police and prosecutors assigned to this investigation in the past also 6 worked conscientiously with laboratory analysts to obtain better results through new approaches and additional tests as they 8 became available. Those efforts ultimately led to the discovery 9 of sufficient genetic markers from this male profile to enter it into the national DNA data bank. 0 In December of 2002, the Boulder District Attorney’s Office, under Mary T. Lacy, assumed responsibility for the inB vestigation of the JonBenét Ramsey homicide. Since then, this U office has worked with the Boulder Police Department to continue the investigation of this crime. In early August of 2007, District Attorney Lacy attended a Continuing Education Program in West Virginia sponsored by the National Institute of Justice on Forensic Biology and DNA. The presenters discussed successful outcomes from a new methodology described as “touch DNA.” One method for sampling for touch DNA is the “scraping method.” In this process, forensic scientists scrape a surface where there is no observable stain or other indication of possible DNA in an effort to recover for analysis any genetic material that might nonetheless be present. This methodology was not well known in this country until recently and is still used infrequently. 399 In October of 2007, we decided to pursue the possibility of submitting additional items from the JonBenét Ramsey homicide to be examined using this methodology. We checked with a number of Colorado sources regarding which private laboratory to use for this work. Based upon multiple recommendations, including that of the Boulder Police Department, we contacted the Bode Technology Group located near Washington, D.C., and initiated discussions with the professionals at that laboratory. First Assistant District Attorney Peter Maguire and Investigator Andy Horita spent a full day with staff members at the Bode facility in early December of 2007. The Bode Technology laboratory applied the “touch DNA” scraping method to both sides of the waist area of the long johns that JonBenét Ramsey was wearing over her underwear when her body was discovered. These sites were chosen because evidence supports the likelihood that the perpetrator removed and/or replaced the long johns, perhaps by handling them on the sides near the waist. On March 24, 2008, Bode informed us that they had recovered and identified genetic material from both sides of the waist area of the long johns. The unknown male profile previously identified from the inside crotch area of the underwear matched the DNA recovered from the long johns at Bode. We consulted with a DNA expert from a different laboratory, who recommended additional investigation into the remote possibility that the DNA might have come from sources at the autopsy when this clothing was removed. Additional samples were obtained and then analyzed by the Colorado Bureau of Investigation to assist us in this effort. We received those results on June 27th of this year and are, as a result, confidant that this DNA did not come from innocent sources at the autopsy. As mentioned above, extensive DNA testing had previously excluded people connected to the family and to the investigation as possible innocent sources. I want to acknowledge my appreciation for the efforts of the Boulder Police Department, Bode Technology Group, the Colorado Bureau of Investigation, and the Denver Police Department Forensic Laboratory for the great work and assistance they have contributed to this investigation. The unexplained third party DNA on the clothing of the victim is very significant and powerful evidence. It is very unlikely that there would be an innocent explanation for DNA found at three different locations on two separate items of clothing worn by the victim at the time of her murder. This is particularly true in this case because the matching DNA profiles were found on genetic material from inside the crotch of the victim’s underwear and near the waist on both sides of her long johns, and because concerted efforts that might identify a source, and perhaps an innocent explanation, were unsuccessful. It is therefore the position of the Boulder District Attorney’s Office that this profile belongs to the perpetrator of the homicide. DNA is very often the most reliable forensic evidence we can hope to find during a criminal investigation. We rely on it often to bring to justice those who have committed crimes. It can likewise be reliable evidence upon which to remove people from suspicion in appropriate cases. (continued ) Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. 400 CHAPTER 15 The Boulder District Attorney’s Office does not consider any member of the Ramsey family, including John, Patsy, or Burke Ramsey, as suspects in this case. We make this announcement now because we have recently obtained this new scientific evidence that adds significantly to the exculpatory value of the previous scientific evidence. We do so with full appreciation for the other evidence in this case. Local, national, and even international publicity has focused on the murder of JonBenét Ramsey. Many members of the public came to believe that one or more of the Ramseys, including her mother or her father or even her brother, were responsible for this brutal homicide. Those suspicions were not based on evidence that had been tested in court; rather, they were based on evidence reported by the media. It is the responsibility of every prosecutor to seek justice. That responsibility includes seeking justice for people whose reputations and lives can be damaged irreparably by the linS gering specter of suspicion. In a highly publicized case, the detrimental impact of publicity and suspicion on people’s livesM can be extreme. The suspicions about the Ramseys in this case created an ongoing living hell for the Ramsey family and theirI friends, which added to their suffering from the unexplained T and devastating loss of JonBenét. For reasons including those discussed above, we believeH that justice dictates that the Ramseys be treated only as victims of this very serious crime. We will accord them all the rights, guaranteed to the victims of violent crimes under the law in Colorado and all the respect and sympathy due from one human being to another. To the extent that this office has added toJ the distress suffered by the Ramsey family at any time or to any O degree, I offer my deepest apology. We prefer that any tips related to this ongoing investigationS be submitted in writing or via electronic mail to BoulderDA.org, but they can also be submitted to our tip line at (303) 441–1636.H This office will make no further statements. Counterpoint U A Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. ISBN: 978-1-323-16745-8 Last year, then–Boulder, Colorado, District Attorney Mary Keenan Lacy, who had been “investigating” the Ramsey case6 for the last few years, wrote a letter to JonBenét’s father John, apologizing for having believed he or his wife, the late Patsy,8 or their son Burke (then nine) had anything to do with their 9 daughter’s 1996 death. Lacy indicated that recent tests from the Bode Laboratory of Virginia revealed that their “new meth-0 odology” of touch DNA found a match that proves an intruder was culpable of the slaying in which the six-year-old was mo-B lested, strangled and given a fractured skull. U There has always been unmatched, unknown male DNA— likely from saliva—in the inside crotch of the child’s underpants. A minute amount, too degraded to get a proper DNA profile, was mixed with her blood when someone stuck her oh-so-slightly with the pointed end of a broken paintbrush on the night of her death. Because the DNA was so insignificant, it was theorized to have come from someone coughing during the manufacturing process, then the blood drops on top rehydrated it. If the DNA and blood were deposited at the same time, they would have degraded at the same rate—but here the blood sample was robust. Lacy wrote that the lab discovered that sloughed-off skin cells on the waist area of the long johns JonBenét wore over her underpants can be matched to the underpants’ DNA. That was great news for people who want to believe there was an intruder with no link to the family members. No one imagines a parent could harm a child in such a brutal and horrendous fashion. Only problem is, adults—including parents—kill kids all the time. While this murder is unique in its application and renown, from an investigative point of view it’s just another homicide that has to be dissected to be understood. Anyone looking rationally at the evidence here, and assessing it as a whole, cannot be pleased with Lacy’s letter to Ramsey or the fact that she cleared the most credible suspects in the case. At the least it sets a terrible precedent where other people “under the umbrella of suspicion” in other cases will demand the same treatment if their investigations take a long time to reach a courtroom. Just because someone isn’t on trial, or a case has gone cold, doesn’t mean that the right people aren’t firmly under the microscope of authorities. Mary Lacy left office in January, 2009, and the new DA, or any in the future, can retract her pronouncement. Frankly it will take a brave person to go against the sea of public opinion by individuals who want to blame a bogeyman. One note of encouragement is the case has been returned to the Boulder police, who are better equipped to investigate than the DA’s office ever was. The case had been moved to Lacy’s predecessor when the Ramsey family complained that the police spotlight on them was unfair. As we all know, there’s no statute of limitations on homicide. This doesn’t take Lacy off the hook, as I see it. Here are some facts of the case which were ignored by her reckless decision. . . . Touch DNA is nothing new to law enforcement, although Bode has only tested for it for about three years. For some ten years, the FBI lab at Quantico and other labs have used it to capture skin cells from inside masks or gloves, and from guns or knives. Neither Lacy nor Bode will make available their test results so independent experts can critically review the information. If scientific evidence is to be used to make an argument, proof should be offered. Perhaps some media outlet will file a lawsuit to compel the documents. What Lacy and Bode have said is that the mystery man’s DNA is on the waist area, and that the DNA doesn’t match any Ramsey family member. Nothing is stated about where and how much Ramsey DNA was discovered. Patsy dressed the child in those long johns before putting her to bed, and the waistband is precisely what John’s two hands touched when he carried his daughter’s stiff body in a vertical position upstairs from the basement where she was found deceased. And since DNA can survive multiple launderings, we can’t pinpoint when that touch DNA was left on the waistband. Boulder County Coroner Dr. John Meyer’s autopsy report is the Rosetta Stone to this case. It explains the type and order of JonBenét’s injuries—asphyxiation by a ligature, then a head blow. It does not reveal who killed the girl. Due to the three-page phony ransom note that many analysts believe was penned by Patsy, the working strategy was to consider Mrs. Ramsey as the perpetrator of all the insults inflicted upon the tot. But while there might have been enough evidence for an arrest, there was not enough for a conviction—and among insiders there was debate about who—if anyone in the household—did what. Without a clear through-line that police and prosecutors could agree upon, what chance would a jury have to find its way to a guilty verdict? What the autopsy report states without equivocation is that the child suffered vaginal injuries that were “chronic,” meaning they predated the murder by days or weeks. We’re talking repeated digital penetration that eroded—not ruptured—her DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL hymen. Also, the opening of her vagina was twice the size of a similar aged child’s. These factors would have been testified to by at least three pediatric gynecological physicians, had the case gone to trial. This unknown pedophile would have needed ongoing intimate access to JonBenét before the night she died. Mary Lacy’s early prosecutorial career was as a sex crimes expert, so why didn’t she recognize the nature of this little girl’s injuries? If some accident led to JonBenét being strangled, then hit violently in the head, a normal reaction would have been for her caretakers to rush her to a hospital. But that didn’t happen, I surmise, because her pre-existing genital injuries would have been noticed. And so, a ridiculous—and sadly, effective—cover-up ensued. Mary Lacy was responsible for the 2006 debacle where she had arrested and brought back from Thailand a false confessor named John Mark Karr. When the underpants’ DNA excluded him from being the perpetrator she let him go and publicly stated: “The DNA could be an artifact. It isn’t necesS sarily the killer’s. There’s a probability that it’s the killer’s. But it could be something else.” M She added: “No one is really cleared of a homicide until there’s a conviction in court, beyond a reasonable doubt. And II don’t think you will get any prosecutor, unless they were presT ent with the person at the time of the crime, to clear someone.” What made her change her thinking when she cleared the H Ramseys? , More to the point, where are the intruder’s skin cells from the rope around the child’s neck, the paintbrush, the spoon and bowl of pineapple she ate from just before she died, the white J blanket that covered her, the flashlight believed to have hit her head, and the pen and paper used in the bogus ransom note? And O where is the intruder’s touch DNA on the waistband of JonBenét’s underpants? Did the stranger pull down her long johns, then comS mand her to pull down her own panties? Are we to believe he then H put on gloves—or maybe a whole scuba suit, since there were no unidentified footprints, finger- or handprints, hairs or fibers? U Woven inside the rope around the neck, which was wrapped around a piece of a broken paintbrush, were fibers A 401 from the distinctive jacket Patsy wore that evening—and, allegedly, inside the underpants were fibers from the wool sweater John had on. Patsy’s fibers were also in the tote where the paintbrush came from and on the sticky side of the piece of duct tape that covered JonBenét’s mouth—a length of tape so small it could have been easily flicked aside by her tongue if it had been placed on her mouth while she was alive. Lacy wrote that autopsy personnel were swabbed and tested for a DNA match, and thus excluded. But what about crime scene workers or lab technicians? And how many markers are in the touch DNA profile? The underpants’ DNA was not enough to get a proper match through CODIS, the federal database. That didn’t stop Lacy from sending it through on a regular basis—such busywork has little prospect of ending with a match, but it makes it seem as if something is being done. Years ago, there was a civil suit in this case wherein a federal judge issued a statement that said, based on her reading of the material submitted to her, there was a higher likelihood of an intruder being the killer than a family member. At that time, Mary Lacy read a statement that suggested the Ramseys were innocent, based on the judicial ruling—though not clearing them. That statement was reportedly dictated to her by a Ramsey associate. What only those close to the case know is that one side of the civil suit completely abandoned its case, never offering paperwork, so the only information the judge had was that which came from the Ramsey camp. Ergo, an easy decision for the judge to make. Since then, Ramsey advisers have pummeled Lacy to clear the family entirely and eventually it happened. It’s egregious when an officer of the court misrepresents scientific evidence to win political favor. Mary Lacy was right to offer up an apology. But it should have been to JonBenét and not her family. Source: Dawna Kaufmann, investigative journalist. Co-author with Cyril H. Wecht, MD, JD, of A Question of Murder, Final Exams: True Crime cases from Cyril Wecht, and From Crime Scene to Courtroom. 6 8 9 0 B U ISBN: 978-1-323-16745-8 chapter summary Portions of the DNA structure are as unique to each individual as fingerprints. The gene is the fundamental unit of heredity. Each gene is actually composed of DNA specifically designed to control the genetic traits of our cells. DNA is constructed as a very large molecule made by linking a series of repeating units called nucleotides. Four types of bases are associated with the DNA structure: adenine (A), guanine (G), cytosine (C), and thymine (T). The bases on each strand are properly aligned in a double-helix configuration. As a result, adenine pairs with thymine and guanine pairs with cytosine. This concept is known as base pairing. The order of the bases is what distinguishes different DNA strands. Portions of the DNA molecule contain sequences of bases that are repeated numerous times. To a forensic scientist, these tandem repeats offer a means of distinguishing one individual from another through DNA typing. Length differences Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. 402 CHAPTER 15 associated with relatively short repeating DNA strands are called short tandem repeats (STRs) and form the basis for the current DNA-typing procedure. They serve as useful markers for identification because they are found in great abundance throughout the human genome. STRs normally consist of repeating sequences 3 to 7 bases long, and the entire strand of an STR is also very short, less than 450 bases long. This means that STRs are much less susceptible to degradation and may often be recovered from bodies or stains that have been subjected to decomposition. Also, because of their shortness, STRs are ideal candidates for multiplication by PCR, in which STR strands are multiplied over a billionfold. PCR is responsible for the ability of STR typing to detect the genetic material of as few as 18 DNA-bearing cells. The more STRs one can characterize, the smaller the percentage of the population from which a particular combination of STRs can emanate. review questions 1. The fundamental unit of heredity is the ___________. 2. Each gene is actually composed of ___________, specifically designed to carry out a single body function. 3. A(n) ___________ is a very large molecule made by linking a series of repeating units. 4. A(n) ___________ is composed of a sugar molecule, a phosphorus-containing group, and a nitrogen-containing molecule called a base. 5. DNA is actually a very large molecule made by linking a series of ___________ to form a natural polymer. S M I T H 15. , True or False: All of the letter sequences in DNA code for the production of proteins. ___________ 16. In STR DNA typing, a typical DNA pattern shows (two, three) bands. 17. True or False: Specimens amenable to DNA typing are blood, semen, body tissues, and hair. ___________ J O S 18. H 19. U A 20. 6 8 9 0 B U 21. 22. 23. 24. 25. Short DNA segments containing repeating sequences of three to seven bases are called ___________. True or False: The longer the DNA strand, the less susceptible it is to degradation. ___________ The short length of STRs allows them to be replicated by ___________. Used as markers for identification purposes, ___________ are locations on the chromosome that contain short sequences that repeat themselves within the DNA molecule and in great abundance throughout the human genome. (CODIS, AFIS) maintains local, state, and national databases of DNA profiles from convicted offenders, unsolved crime-scene evidence, and profiles of missing people. Amazingly, the sensitivity of STR profiling requires only ___________ DNA-bearing cells to obtain an STR profile. During evidence collection, all body fluids must be assumed to be ___________ and handled with latexgloved hands. The concept of (CODIS, multiplexing) involves simultaneous detection of more than one DNA marker. Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc. ISBN: 978-1-323-16745-8 6. ___________ different bases are associated with the makeup of DNA. 7. Watson and Crick demonstrated that DNA is composed of two strands coiled into the shape of a(n) ___________. 8. The structure of DNA requires the pairing of base A to ___________ and base G to ___________. 9. The base sequence T–G–C–A can be paired with the base sequence ___________ in a double-helix configuration. 10. The inheritable traits that are controlled by DNA arise out of DNA’s ability to direct the production of ___________. 11. ___________ are derived from a combination of up to 20 known amino acids. 12. The production of an amino acid is controlled by a sequence of ___________ bases on the DNA molecule. 13. True or False: Enzymes known as DNA polymerase assemble new DNA strands into a proper base sequence during replication. ___________ 14. True or False: DNA can be copied outside a living cell. ___________ This gives rise to the concept of multiplexing. Using the technology of PCR, one can simultaneously extract and amplify a combination of different STRs. Currently, U.S. crime laboratories have standardized on 13 STRs. With STR analysis, as few as 125 picograms of DNA are required. Another type of DNA used for individual characterization is mitochondrial DNA. Mitochondrial DNA is located outside the cell’s nucleus and is inherited from the mother. However, mitochondrial DNA typing does not approach STR analysis in its discrimination power and thus is best reserved for samples, such as hair, for which STR analysis may not be possible. Bloodstained evidence should not be packaged in plastic or airtight containers because accumulation of residual moisture could contribute to the growth of blood-destroying bacteria and fungi. Each stained article should be packaged separately in a paper bag or in a well-ventilated box. DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL 26. The amelogenin gene shows two bands for a (male, female) and one band for a (male, female). 27. Y-STR typing is useful when one is confronted with a DNA mixture containing more than one (male, female) contributor. 403 31. True or False: Y-STR data is normally entered into the CODIS database collection. ___________. 32. Small amounts of blood are best submitted to a crime laboratory in a (wet, dry) condition. 33. True or False: Airtight packages make the best containers for blood-containing evidence. ___________ 28. Mitochondrial DNA is inherited from the (mother, father). 29. True or False: Mitochondrial DNA is more plentiful in the human cell than is nuclear DNA. ___________ 34. Whole blood collected for DNA-typing purposes must be placed in a vacuum containing the preservative ___________. 35. A typical STR DNA type emanating from a single individual shows a (one, two, three)-band pattern. 30. The national DNA database in the United States has standardized on ___________ STRs for entry into the database. S review questions for inside the science 1. True or False: Enzymes known as DNA polymerases assemble new DNA strands into a proper base sequence based off the template strand during replication. ___________ 2. DNA evidence at a crime scene can be copied by the processes of the ___________ with the aid of a DNA polymerase and specific primers. application and critical 1. The following sequence of bases is located strand of a DNA molecule: M ...
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Running head: FORENSIC SCIENCE

Forensic Science
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FORENSIC SCIENCE

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Discussion

DNA is an organic chemical uniquely designed to carry out a single body function. DNA
in simpler terms codes genetic information for the transmission of genes in all living cells
whether plant or animal, Hu, N (2014). DNA was first discovered in 1868 but a scientist could
not clearly comprehend its role until the 1950’s when the function of DNA was established by
James Watson and Francis Crick. Over the years several advancements have been made in the
field. Most notably is the replication of DNA. Naturally, the body is able to duplicate DNA but
not until recently was it possible to replicate DNA in the laboratories. However, through
polymerase chain reaction (PCR) small quantities or broken pieces of DNA found in a crime
scene can now be duplicated to a quantity that can be used for analysis (Hu et al., 2014). This
means that the sample size no longer matters in terms of DNA evidence collected at a crime
scene.
DNA evidence can also be subjected to short tandem repeats (STR) for profiling since
they help distinguish one individual from the other through typing. Tandem repeats can be
defined as repeating sequences in DNA segments that seem to act as a filler or spacers between
DNA coding. According to Vitelli, (2017), in the US, 13 STR markers are used in forensic DNA
profiling as they provide a high degree of polymorphism making them of particular use in
forensic science. Mostly penta- and tetra-nucleotide repeats are the most commonly used for
profiling as they tend to be more robust (Vitelli, 2017).
Case Summary
Timothy McVeigh was an American domestic terrorist who used a bomb to kill about
168 people including infants who were at the daycare center in Alfred P Murray building. ...


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