Inheritance Lab Directions and Background Updated 5/14/14 Introduction to the Inheritance Lab In this lab you will: 1) Observe and report your phenotype for the several Mendelian traits (listed below.) 2) Infer and report your genotype or possible genotypes for each trait using your understanding of recessive and dominant characteristics. 3) Infer and report all of the possible parental crosses that could have led to your possible genotypes by applying the logic of Mendelian genetics. Please read the relevant sections of your textbook on Mendelian genetics and Punnett squares before proceeding with this lab. Use your text or an online search to learn the following vocabulary terms: phenotype, genotype, gene, allele, dominant allele, recessive allele, gamete, genetic cross, heterozygous, and homozygous. Be sure to save the Inheritance Lab Report document to your computer so you may complete an electronic version of the report. You submit this to your Instructor for your Lab Assignment for this week. © 2012 Laureate Education, Inc. Part 1. Phenotypes For this part of the lab you will observe and report about some of your phenotypic traits. Each phenotypic trait is associated with a letter. If you have the dominant allele for a given trait, you would use the uppercase letter associated with the trait to report that phenotype in your lab report. On the other hand, if you have the recessive allele for that trait you would use the lowercase letter to report your phenotype for that trait. You will also use this convention when identifying alleles in your possible genotypes (more about this in part 2.) An example of a Mendelian trait (which we will do not analyze in the lab report) is the cleft chin, which is associated with the letter “c”. Cleft chins refer to the central dimple that some people exhibit in the chin. Cleft chins are the result of a dominant allele for this trait. If you have the dominant allele for the cleft chin you would use the uppercase “C” to report that phenotype. If you do not have a cleft chin, this is associated with the recessive allele and it is reported as the lowercase “c”. Traits to be Analyzed Each of the five traits that you will analyze in the lab are explained below. These traits include earlobe attachment or lack of attachment to the head, the presence or absence of dimples, the ability or lack of ability to roll your tongue, and the presence or absence of a widow’s peak. EARLOBES Having free earlobes is a dominant trait (E); having attached earlobes is a recessive trait (e). Explanation: A free earlobe hangs below the point where the ear attaches to the head. An attached earlobe attaches directly to the side of the head. © 2012 Laureate Education, Inc. DIMPLES Having dimples is a dominant trait (D); not having dimples is recessive (d). Explanation: Dimples are natural indentations in the face on either side of the mouth. (A person may have just one dimple on one side of the mouth.) TONGUE ROLLING The ability to roll up the sides of the tongue is dominant (T); not having the ability to roll up the sides of the tongue is recessive (t). . © 2012 Laureate Education, Inc. TOE LENGTH ON FOOT Having a second toe longer than the foot’s big toe is a dominant trait (F); having a second toe shorter than the foot’s big toe is a recessive trait (f). Explanation: The second toe in the above statement refers to the toe that is adjacent (next to) the big toe on your foot. If the second toe is longer than the big toe, you have the dominant trait; if the second toe is shorter than the big toe, you have the recessive trait. WIDOW’S PEAK Having a distinct point in the hairline at the top of the face is a dominant trait (W); not having a distinct point in the hairline at the top of the face is a recessive trait (w). © 2012 Laureate Education, Inc. Part 2 Genotypes Your phenotype represents the traits that visibly express themselves in your body. However because you inherit an allele from both of your parents and thus carry two alleles for each trait it is possible that some of the alleles that you carry in your genome are not readily observed by looking in a mirror. Alleles that are recessive will not be visible if you also carry a dominant allele. Thus if you inherited a dominant allele from one parent and a recessive allele from the other parent you will show the trait associated with the dominant trait but not the trait associated with the recessive allele. In the case of phenotypes you use a single letter to represent the observed trait but in the case of genotypes we must use two letters to represent the two alleles that you carry in your genome. As we learned in part 1 the presence of a cleft chin represents a dominant allele and if you have a cleft chin you would represent your phenotype with regards to this trait as an uppercase “C” whereas if you do not show this trait then you would represent this trait as a lowercase “c”. By definition, if you do not have a cleft chin you can infer that you do not carry the dominant allele for this trait because if you did you would see it in your phenotype. Thus a person without a cleft chin can infer that they received the recessive allele for this trait from both of their parents and that your genotype is a “cc” meaning that they have two recessive alleles. In the other situation, where your phenotype is a “C” (i.e. you would show the dominant trait of having a cleft chin) then you are not certain if you inherited the dominant allele from both parents or if you inherited a dominant allele from only one parent and a recessive allele from the other. In this case you can infer tha t your genotype is either “CC” or “Cc” referring to each of these cases respectively. Part 3 Parental Crosses BACKGROUND ON MENDELIAN GENETICS When traits are the result of a single gene with a few distinct alleles, you may use the logic of Mendelian genetics to predict the genotypes of offspring. To apply Mendelian genetics, you must understand the following terms: genotype, phenotype, dominant allele, recessive allele, heterozygous, homozygous, and Punnett square. Here is an example of a Punnett square. In this analysis, we will use our example of the cleft chin. The dominant allele for this trait is having a cleft chin “C” and the recessive allele is not showing a cleft chin “c”. Consider the case where a heterozygous parent with a genotype of Cc mates with a homozygous parent who has an cc genotype. Such a cross is represented as Cc x cc . 1. Set up the square: To analyze the possible offspring from this paring CC x Cc we take the two alleles of each parent (representing the types of gametes that each produces) and place them along the sides of our Punnett square. c C c © 2012 Laureate Education, Inc. c 2. Fill in the square: With the alleles from the two types of gametes produced by the homozygous parent (c and c) along the top of the square and the alleles carried by the gametes produced by the heterozygous parent (C and c) along the sides of the square, we can now fill in what would happen when the gametes from one parent meet with the other. In this case the homozygous parent contributes a “c” to each cell in the square while the heterozygous parent contributes a “C” in the upper row and a “c” in the lower row. The four possible combinations in each cell represent the types of fertilized eggs that can be produced by this cross (Cc x cc) c c C Cc Cc c cc cc 3. Interpreting the Square: The four cells of the square represent the four possible types of offspring that could be produced in the pairing and each cell is equally probable. Based on this, what percentage of the offspring in the Punnett square above will display a cleft chin? (answer below) You may also use Mendelian genetics to infer possible genotypes of parents based on the phenotype of a child. For example, if a child displays a cleft chin, what are his or her possible genotypes? (Hint: There are two possible genotypes.) Based on this answer, what possible crosses might the parents have? Continuing with the above example, if you have a cleft chin, your phenotype is C, but what is your genotype? Both a “CC” and a “Cc” individual would display a cleft chin, so your genotype could be either of these. Using Mendelian genetics, you can infer the different possible pairings of parental phenotypes that would lead to your genotypes. For example, let’s examine the case in which you are a heterozygote for a cleft chin and consider what possible parental crosses could have resulted in the Cc genotype. Notice that we are leaving the “CC” case as an exercise for you. All of the following parental crosses could lead to a “Cc” offspring: CC x Cc CC x cc Cc x Cc Cc x cc Does this make sense? If not, run a Punnett square on each cross. (See pages 157–158 in your course text for how to use a Punnett square.) You may also practice using a Punnett square by referring to the Punnett square calculator listed in the Optional Resources section.) You can also predict which of the above crosses would be most likely by considering which of these pairings is most likely to give an Cc offspring (e.g., 25%, 50%, or 100% probability). After identifying your possible genotypes you will use this logic to infer all of the possible crosses that could have led to your possible genotypes. Answer: Two of the gametes produced have “cc” genotypes and two have “Cc”. Each cell has a 25% likelihood of occurring so there is a 50% chance that an offspring from this cross will have a cleft chin. © 2012 Laureate Education, Inc. Inheritance Lab Report Name: ________________________ Date: _________________________ Updated 5/15/2014 Purpose To develop and apply an understanding Mendelian inheritance patterns and Punnett squares. Preparation (4 points) Review the background document on inheritance and describe the concepts of dominant and recessive alleles, gametes, phenotype and genotypes. Materials and Methods Read the Inheritance Lab Background materials. No other materials are required for this lab. You will observe a variety of phenotypic characteristics in yourself and record these in the table in the Results section below. Using the logic of Mendelian genetics, you will then record your possible genotypes, as well as your parents’ possible genotypes. Do not refer to your parent’s phenotypes in order to infer the possible crosses that could have led to your phenotype. Complete the following steps, and record your findings in the table in the Results section. 1. Record each of your phenotypes in the Your Phenotype column. Identify your phenotype using a single letter for eazch trait as indicated below (capital letter indicates dominant allele, lowercase indicates recessive allele): • E – free earlobes; e – attached earlobes • D – dimples; d – no dimples • T – able to roll tongue; t – not able to roll tongue • F – second toe longer than big toe; f – second toe shorter than big toe • W – widow’s peak; w – no widow’s peak 2. Identify and record your possible genotypes based on your phenotypes. Genotypes are represented using two alleles. Identify the alleles using the letters indicated below (capital letter indicates dominant allele, lowercase indicates recessive allele): • E – free earlobes; e – attached earlobes • D – dimples; d – no dimples • T – able to roll tongue; t – not able to roll tongue • F – second toe longer than big toe; f – second toe shorter than big toe • W – widow’s peak; w – no widow’s peak 3. Using your possible genotypes, identify and record all of the possible pairings of parental genotypes that could have led to your possible genotypes. Crosses are denoted in this form: FF x Ff and indicates the genotypes of both parents. You should list all of the possible crosses that could lead to your phenotype. Inheritance Lab Report - 1 © 2012 Laureate Education, Inc. Preliminary Analysis (4 points) Describe how a genetic trait can skip one or more generations without being apparent. How might one learn about unseen alleles in a child’s parents by observing traits in the child? Results (26 points) Use the chart below to record the observations of your phenotypes and to record your inferences regarding your genotype and all of the possible crossings of parental genotypes that can account for your genotype. Phenotypes are expressed with a single letter related to the trait. Genotypes include both alleles and are, thus, expressed with two letters (one for each allele). Possible parental genotypes and crosses consist of two genotypes crossed. For instance, a freckled person will have a phenotype of F and possible genotypes of FF and Ff. One of the possible parental genotype and crosses is (FF x Ff). Be sure to list all possible parental genotypes in terms of possible crosses. Crosses are denoted in this form: FF x Ff and you should list all of the possible crosses that could lead to your phenotype. Physical Characteristic Earlobes: Free or Attached Dimples Your Phenotype Your Genotype or Possible Genotypes All Possible Parental Crosses Tongue Rolling Second Toe Longer Than Big Toe on Foot Widow’s Peak Analysis (12 points) Write an analysis of two or more paragraphs that includes the following: • A summary of your results and the overall knowledge you gained from this lab • Explain the cellular basis for one component of your genotype coming from each parent. • Describe how Punnett squares are related to cell division. • An example of how Mendelian logic could be useful Inheritance Lab Report - 2 © 2012 Laureate Education, Inc. Conclusion (4 points) Write a conclusion of two or more paragraphs that includes the following: • A brief recap of the main points in your analysis • Propose a research question about this lab topic that you would like to answer in the future. Inheritance Lab Report - 3 © 2012 Laureate Education, Inc. Inheritance Lab Background Background on Mendelian Genetics When traits are the result of a single gene with a few distinct alleles, you may use the logic of Mendelian genetics to predict the genotypes of offspring. To apply Mendelian genetics, you must understand the following terms: genotype, phenotype, dominant allele, recessive allele, heterozygous, homozygous, and Punnett square. Here is an example of a Punnett square. In this example, we will assume that having freckles is a simple single allele example of Mendelian genetics and that the dominant allele is freckles (F) and the recessive allele is no freckles (f). A heterozygous parent with a genotype of Ff mates with a homozygous parent who has an ff genotype. This is an example: f f F Ff Ff f ff ff Based on what you know about Mendelian genetics, what percentage of the offspring in the Punnett square above will display freckles? You may also use Mendelian genetics to infer possible genotypes of parents based on the phenotype of a child. For example, if a child displays freckles, what are his or her possible genotypes? (Hint: There are two possible genotypes.) Based on this answer, what genotypes might the parents have? (Hint: There are more than two possible genotypes for the parents.) Continuing with the above example, imagine that you do not know your birth parents and have no siblings, but that you do have freckles. Thus, your phenotype is F, but what is your genotype? Both an FF and an Ff individual would display freckles, so your genotype could be either of these. Using Mendelian genetics, you can infer the different possible pairings of parental phenotypes that would lead to your genotypes. For instance, let’s examine the case in which you are a heterozygote for freckles and consider what possible parental crosses could have resulted in the Ff genotype. Any of the following parental crosses are possible: FF x Ff FF x ff Ff x Ff Does this make sense? If not, run a Punnett square on each cross. (See pages 157–158 in your course text for how to use a Punnett square. You may also practice using a Punnett square by referring to the Punnett square calculator listed in the Optional Resources section.) You can also predict which of the above crosses would be most likely by considering which of these pairings is most likely to give an Ff offspring (e.g., 25%, 50%, or 100% probability). You will use this logic by identifying several particular phenotypes and then infer your parents’ possible genotypes. © 2012 Laureate Education, Inc. BACKGROUND ON PHENOTYPES For this lab, you will identify your phenotype for a variety of physical characteristics, and infer your possible genotypes based on the phenotype. Then you will infer possible genotypes for each of your parents. Save the Inheritance Lab Report document to your computer so you may complete an electronic version of the report. You submit this to your Instructor for your Application Assignment for this week. The following are the phenotypes you will identify in the lab report. When identifying the possible genotypes, use the letters listed below for the dominant and recessive alleles. EARLOBES Having free earlobes is a dominant trait (E); having attached earlobes is a recessive trait (e). Explanation: A free earlobe hangs below the point where the ear attaches to the head. An attached earlobe attaches directly to the side of the head. DIMPLES Having dimples is a dominant trait (D); not having dimples is recessive (d). Explanation: Dimples are natural indentations in the face on either side of the mouth. (A person may have just one dimple on one side of the mouth.) © 2012 Laureate Education, Inc. TONGUE ROLLING The ability to roll up the sides of the tongue is dominant (T); not having the ability to roll up the sides of the tongue is recessive (t). © 2012 Laureate Education, Inc. TOE LENGTH ON FOOT Having a second toe longer than the foot’s big toe is a dominant trait (F); having a second toe shorter than the foot’s big toe is a recessive trait (f). Explanation: The second toe in the above statement refers to the toe that is adjacent (next to) the big toe on your foot. If the second toe is longer than the big toe, you have the dominant trait; if the second toe is shorter than the big toe, you have the recessive trait. WIDOW’S PEAK Having a distinct point in the hairline at the top of the face is a dominant trait (W); not having a distinct point in the hairline at the top of the face is a recessive trait (w). © 2012 Laureate Education, Inc. 
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