23rd November, 2018
Crime scene Investigation
Distinguishing blood types
DNA (DeoxyriboNucleic Acid) is within our genetic material. It is found in all living organisms
from bacteria to humans. DNA is replicated before mitosis and repaired when damaged. The
DNA that we have comes from our parents, and leads to the genes present in all our cells. The
DNA in cells is transcribed to mRNA, which is translated to proteins needed. Cells are present in
fluids left at crime scenes, and most contain DNA. DNA is found in blood, semen, skin cells,
muscle, brain cells, bone teeth, hair, saliva, mucus, perspiration, fingernails, urine, and feces.
DNA is also useful for parentage testing and archeological remains testing. The amount of DNA
present depends on the fluid left behind.
At crime scenes, DNA is used to vindicate or incriminate suspects. The genetic fingerprint,
which is the DNA sequence, identifies individuals but not for identical twins. Apart from DNA
testing, Blood tests can also be used to identify individuals, based on the different blood types
that exist. Blood antigens found on the surface of red blood cells can be used to classify the
blood types of blood found in crime scenes.
1. Which chapters in your book relate to this lab?
2. What are the independent and dependent variables?
An independent variable is that which does not changes in the experiment. In this case, the
independent variable was the blood type of the people what was tested. The dependent variables
were the blood types which change depending on the blood that is tested.
3. Do all our cells have the same DNA?
All our cells do not have the same DNA. Our DNA is unique and mostly dependent on
inheritance from our parents.
4. What parts of DNA are used for parental tests and why?
The sequence of DNA is used for parental tests. The way the DNA is organized, the pattern of
DNA is studied to determine one’s blood relation.
5. Which other tests can be used for blood? Which other tests can be used for saliva?
Blood can be tested for nucleic acids such as DNA, ABO blood typing, human Glycophorin A
and human hemoglobin. The test done for saliva is usually alpha-amylase test.
Four dishes with three wells each
- Anti-B serum
Four blood samples
- Anti-D serum
Sample 2 (Chris)
- Paper towels
Sample 3 (Lisa)
- Wax pencils
Sample 4 (Thomas)
1. Get four dishes with three test wells each and label them 1,2,3,4.
2. Add 2 drops of blood sample 1 to all three wells of dish 1
3. Add 2 drops of sample 2 to three wells of dish 2.
4. Add 2 drops of sample 3 to three wells of di...