PopGenProbSet_1_Spr_2009 - Name _______________________...

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Unformatted text preview: Name _______________________ BioEE 2780 Section _________ Population Genetics Problem Set I The completed problem set is due before lecture Thursday, April 2nd. This assignment is worth a total of 15 points and you must show your work to receive full credit. Write or type your answers on a separate sheet. Problem 1. In 1941, 24 miles of security fencing were installed to enclose a natural conservation area at the site of a former U.S. Army depot not far from here in Seneca County, New York. Within a few years, however, something unique happened. White pigmented deer began showing up in the herds living near the depot. Today, the Seneca Conservation Area is home to the world's largest group of white deer, nearly 200 individuals strong. Such a density of white deer can be found nowhere else in the world. (True story! The above modified from http://www.senecawhitedeer.org/history/whitedeer.php). You are a student interested in studying the evolution and population genetics of this coat color polymorphism. You suspect that natural selection plays a role in maintaining this polymorphism, but Dr. Zamudio is skeptical. A Seneca county official doing fieldwork in the conservation area sends you data on genotype and coat color phenotype and for 274 deer. You show Dr. Zamudio the data and she says, "The first thing you need to do to convince me about your `selection' hypothesis is check for Hardy-Weinberg Equilibrium!" Deer Data: Seneca Conservation Area Genotype AA Aa aa Color White Light Brown Brown Number 96 104 74 (A) Briefly explain why Dr. Zamudio wants to know about Hardy-Weinberg Equilibrium (HWE) in this population. Why is this informative regarding your hypothesis that natural selection shapes the frequency of color polymorphism among the deer in the Seneca Conservation Area? (B) Being the dutiful student that you are, you immediately do as Dr. Zamudio suggests. Calculate allele frequencies and expected genotype frequencies for this sample and address the following questions: How do observed and expected numbers of genotypes differ? Does it appear that the deer population is in Hardy-Weinberg equilibrium? Does this support your assertion about natural selection acting on the deer population or Dr. Zamudio's skepticism about it? Explain why. Assuming the deer population is not in HWE (regardless of the observed data) which evolutionary processes other than selection could account for this? (Hint: there are four such processes.) 1 Name _______________________ Section _________ On closer inspection of your colleague's field records, you discover that 130 of the deer were recorded at locations inside the security fence surrounding the conservation area, and the remaining 144 deer were recorded at locations outside the fence. Phenotypes for deer from the two areas are: Inside Fence Color Number White 82 Light Brown 42 Brown 6 Outside Fence Color Number White 14 Light Brown 62 Brown 68 (C) Calculate allele and expected genotype frequencies for the `inside' and `outside' groups. Is each of these groups in Hardy-Weinberg equilibrium? (D) Do these new results offer further support for your `selection' hypothesis, or will Dr. Zamudio be saying `I told you so!' at your next meeting? Justify your answer. (E) What do these results tell you about the probable effect of installing the security fence on the deer living in the area? (Hint: What can we say about gene flow (migration) between groups of deer living inside and outside the fence?) Problem 2. The following news story appeared around the country in January of this year: Baby Born In Bay Area With 12 Functioning Fingers, 12 Toes -- DALY CITY, Calif. -A Daly City couple is beaming after becoming the proud parents of a healthy but incredibly rare baby boy this month. Baby Kamani Hubbard has sixfully formed and functional fingers and toes on his hands and feet. It's called "polydactyly" -- extra digits -- not an uncommon genetic trait, but Bay Area doctors say they've never seen a case so remarkable. . ." (http://www.ktvu.com/news/18608582/detail.html#) The condition of having extra fingers and/or toes (either partial or fully formed) occurs in 2 children out of every 1000 live births on average in humans. Many people are surprised to learn that polydactyly is caused by a single dominant (rather than recessive) allele of a gene that controls the development of digits. In light of what you know about HWE, how would you explain to a friend why polydactyly is not more common in the human population? (Generally, what does the Hardy-Weinberg model show us about the impact of an allele's dominance on its frequency in a population?) 2 ...
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