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BIO109 – Human Genetic Traits Laboratory Activity Name: Purpose: The purpose of this exercise is to allow you to determine your own phenotype and possible genotypes for several clear-cut observable genetic traits and to study the genetic patterns of a population by comparing your complement of selected traits with those of your classmates (a limited population). Introduction: It is comforting to learn that there is no one else on Earth quite like you. Even though there are billions of people around the world, most of us can recognize our acquaintances quickly and accurately be a mere superficial glance. Even our voices are unique and recognizable. It is known that much of our individuality is in genetic in origin because we each have a combination of genes that is uniquely our own. Thus because of the almost infinite possible combinations of traits in humans, every individual is unique- with the exception of identical twins. (Even identical twins are not absolutely alike due to some modifications of their genes influenced by environment.) Exercise I – Definitions Using the space below, provide a definition of each of the terms below. You will be able to find definitions for these terms in your textbook. Genetic trait: Click here to enter text. Gene: Click here to enter text. Allele: Click here to enter text. Genotype: Click here to enter text. Phenotype: Click here to enter text. Homozygous Click here to enter text. Heterozygous Click here to enter text. Dominant: Click here to enter text. Recessive: Click here to enter text. Exercise II – Human Genetic Traits This lab is designed to demonstrate genetics, or the study of how heritable characteristics are passed from generation to generation. Genetic traits are determined by genes, or small segments of DNA carried on chromosomes that determine physical characteristics. This exercise demonstrates how different alleles of the same gene segregate in an individual and how traits occur in a population. Some human traits exhibit the simple dominant and recessive behavior of a monohybrid cross similar to Mendel's peas. However, the expression of many other human traits, like skin color or height, is much more complex and the genetics cannot be easily studied. We will look at a few easily observed human genetic traits to illustrate the simple dominant-recessive relationship between alleles in humans. Traits: 418147512065Tongue Rolling: In 1940, the famous geneticist Alfred Sturtevant noted that about 70% of people of European ancestry are able to roll up the lateral edges of the tongue, while the remaining 30% were unable to do so. Tongue rolling ability may be due to a single gene with the ability to roll the tongue a dominant allele (R) and the lack of tongue rolling ability a recessive allele (r). 45910500Widow’s Peak: Examine the hairline on your forehead. Determine if you have a widows peak, or a straight or curved hairline. The (W) allele for a widow’s peak is dominant over the (w) allele for a straight hairline. 4667250259080 46672501243330Attached Earlobes: If earlobes hang free, they are detached. If they attach directly to the side of the head, they are attached earlobes. Some scientists have reported that this trait is due to a single gene for which unattached earlobes is dominant (E) and attached earlobes is recessive (e). Facial Dimples: Dimples are reportedly due to a single gene with dimples dominant (D; people may exhibit a dimple on only one side of the face) and a lack of dimples recessive (d). 48577501597025466725000057727850Mid-Digit Hair: Some people have hair on the middle digits on the back of their fingers (the second, middle joint) while others do not. The complete absence of hair from all fingers is due to the recessive gene, (m). The presence of mid-digital hair is due to the dominant allele (M). Bent Little Finger: Hold your hands before your face so that your palms are toward you. Place your two little fingers side by side. Determine whether they run parallel to each other for their entire length or if the terminal digits bend out away from each other. The (B) allele for bent little finger is dominant over the (b) allele for a straight little finger. 48196509525Hitchhiker’s Thumb: This trait can be determined by bending the last joint of the thumb as far back as possible. Some people can bend it back at an angle of 60 degrees or more. The ability to bend the thumb back this far is determined by the dominant gene (H), whereas the lack of ability to bend is determined by the recessive allele (h). 4781550-205740Cleft Chin: This trait is reportedly due to a single gene with a cleft chin (C) dominant and a smooth (c) chin recessive. Observations: Using the descriptions above, determine your phenotype and complete the table below. Complete the ‘My Phenotype’ column by entering the physical appearance you have for each trait. Under ‘My Genotype’ place an X in one of the two columns; if you exhibit the dominant trait, place a checkmark in the ‘Homozygous Dominant OR Heterozygous’ column; if you exhibit the recessive trait, place a checkmark in the ‘Homozygous Recessive’ column. Trait My Genotype Dominant Recessive My Phenotype Homozygous Dominant OR Heterozygous Homozygous Recessive Tongue Rolling (R) Non-Tongue Rolling (r) Click here to enter text. ? ? Widow’s Peak (W) Straight Hair Line (w) Click here to enter text. ? ? Unattached Earlobes (E) Attached Earlobes (e) Click here to enter text. ? ? Dimples (D) No dimples (d) Click here to enter text. ? ? Mid-digit Hair (M) No mid-digit hair (m) Click here to enter text. ? ? Bent Little Finger (B) Straight Little Finger (b) Click here to enter text. ? ? Hitchhiker’s Thumb (H) Straight Thumb (h) Click here to enter text. ? ? Cleft chin (C) Smooth chin (c) Click here to enter text. ? ? Exercise III – Human Genetic Traits in a Population Early in the twentieth century mathematician Godfrey Hardy and physician Wilhelm Weinberg independently developed a model describing the relationship between the frequency of the dominant and recessive alleles in a population. They reasoned that the combined frequencies of dominant and recessive alleles must equal 100%, since together they represent all the alleles for that trait in the population. In their model, they assigned the frequency of the dominant allele as (P) and the frequency of the recessive allele as (q). In this case, we can decipher that (P) + (q) = 1 for a population (100% of the alleles are either P or q). They then determined that: The percentage of Homozygous Dominant individuals can be estimated as (P2). The percentage of Heterozygous individuals can be estimated as (2xPxq). The percentage of Homozygous Recessive individuals can be estimated as (q2). The usefulness of these equations is the fact that we can determine the percentage of Homozygous Recessive individuals easily since their phenotype is identifiable. If we know the percentage of Homozygous Recessive individuals in a population, we can then calculate the frequency of the recessive (q) allele since this will be equal to the square root of the percentage of Homozygous Recessive individuals. Once we know the frequency of the recessive (q) allele in a population, we can calculate the frequency of the dominant (P) allele since (P) + (q) = 1 (therefore, (P) = 1-(q). right889000With both the frequencies of the dominant (P) and (q) alleles calculated, we can estimate the number of Homozygous Dominant (P2), the number of Heterozygous (2xPxq) and the number of Homozygous Recessive (q2) individuals as well. For this activity, you will be asked to enter your results onto a shared spreadsheet that will be available to the entire class. In the spreadsheet, you will be entering your name on the next available row and then placing an ‘x’ in each column where you ‘have’ the recessive trait. The spreadsheet is set up so that it will automatically calculate the allele and genotype frequencies as everyone enters their results. ENTER ALL YOUR INDIVIDUAL RESULTS INTO THE CLASS SPREADSHEET BY THURSDAY, MIDNIGHT, EST. FOR SATURDAY: After all of the students’ data have been entered, please revisit the spreadsheet to answer the questions below: What percentage of the class is Homozygous Dominant (RR) for the Tongue-Rolling trait? What percentage of the class is Heterozygous (Ee) for the Free Earlobe trait? What percentage of the class is Homozygous Dominant (MM) for the Mid-Digit Hair trait? What percentage of the class is Heterozygous (Hh) for the Hitchhiker Thumb trait? What percentage of the class is Homozygous Recessive (cc) for the Smooth Chin trait? Exercise IV – Questions Is a person abnormal who expresses the recessive characteristic of a trait? Support your answer by using scientific explanations. Curly hair (h) shows a lack of dominance over straight hair (H), and the heterozygote possessing wavy hair (Hh). If two people with wavy hair marry, what hair types would you expect to find among their children? List the proportion (percentage) of each hair type. (Hint: drawing a Punnett Square may help you answer this question) What is the genotype of a woman who has free ear lobes but whose father has attached ear lobes? Please demonstrate how you arrived at your answer. Could two parents who cannot roll their tongues have children who can roll their tongues? Explain your answer: Every so often the Ann Landers column has a letter from a mother whose husband and in-laws have been chiding her for having daughters instead of sons. Is this criticism justified? Why or why not?