POPULATION GENETICS PROBLEM SET 1 BIOLOGY 201 FALL 2014 Answer all of the following problems Show calculations as well as results 1 HWE Electrophoresis was used to study the gene for phosphoglucose isomerase 2 in the evening primrose Oenothera biennis Two alleles A and a were observed that affected electrophoretic mobility of the enzyme and 40 AA 2 Aa and 18 aa genotypes were found among 60 individuals a Calculate the allele frequencies p f A and q f a b What numbers of the genotypes would be expected if the HW assumption were met Is this population in HWE c 2 HWE Tay Sachs is a recessive genetic disease that is lethal in early childhood Among Jews in the United States about 1 in 2 800 children are affected Assuming random mating among US Jews what is the frequency of heterozygous carriers 3 HWE An experimental population of Drosophila melanogaster is started with 100 AA females and 100 aa males a What will be the genotype frequencies in the F1 and F2 generations assuming random mating and that all genotypes reproduce and survive equally well b What about the F3 generation Hint It is possible to answer this question without math 1 4 Genetic Variation Polymorphism and Heterozygosity are measures of genetic variation that can be used to monitor the health of endangered populations Individuals in an endangered population of sage grouse were genotyped at 5 loci Locus 1 2 3 4 5 Genotype Aa 0 0 9 2 0 AA 100 100 52 13 100 aa 0 0 39 85 0 Total 100 100 100 100 100 a Calculate polymorphism and heterozygosity for this population b For healthy populations of sage grouse living in other parts of the world typical values are P 45 and H 12 Give an explanation for why polymorphism and heterozygosity differ in this endangered population 5 Evolution by Natural Selection a List Darwin s four postulates i ii iii iv b Describe at least two challenges faced by biologists who apply these postulates to wild populations Be creative 6 Natural Selection and Genetic Variation Natural selection removes individuals from a population that have less adapted traits generally decreasing genetic variation But variation is necessary to achieve evolution by natural selection What natural processes can resolve this paradox In other words what natural processes can explain why genetic variation persists in the face of continuing operation of natural selection Describe at least two 2 7 Natural Selection Suppose that in a wild population of walking sticks we find an allele A for brown coloration that makes individuals with two copies twice as camouflaged as individuals with no copies Individuals with one copy of the camouflage allele are intermediate Using our data we construct this fitness table Genotype Phenotype Fitness AA Camouflaged 1 aa Conspicuous 1 2s Aa Intermediate 1 s Let p be the frequency of the A allele and derive an expression for p the frequency of A in the next generation You must write down an expression for p but you do not have to simplify it 8 Natural Selection A new mutation at the T locus has arisen in the squirrel population on UNC s campus The allele makes the coats of heterozygotes Carolina blue A curious undergraduate wonders if there is a selection advantage due to students giving these squirrels extra food handouts He counts the number of each genotype in early summer just following a breeding and again just before breeding in the winter His results were as follows Genotype Phenotype born in June alive at reproductive maturity in November TT White 3500 1600 Tt Carolina Blue 400 350 tt Duke Blue 250 100 a Calculate the Absolute Fitnesses of the three genotypes TT Tt and tt b Calculate the Relative Fitnesses of the three genotypes TT Tt and tt c What will the equilibrium frequency of the T allele be in this population if this trend continues for many many generations 3