Student number:


MID-TERM BIO 434: October 16, 1997
























1. What processes can increase the amount of genetic variance in a population? What processes can decrease genetic variance?



2. The relative fitnesses of two alleles in a haploid organism are 1-ps and 1-qs, where p and q are the allele frequencies and s>0. What is this an example of?




3. The frequency of individuals with a genetic disease phenotype at birth in a large, randomly-mating population is 0.000001. It is known that the mutation rate for the allele which causes this disease is 10-7. If the allele is completely recessive, what can we infer about the strength of selection against homozygotes for the deleterious allele? If the allele is not completely recessive, what can we infer about the strength of selection against homozygotes for the deleterious allele?









4. What is the approximate mutation load associated with an incompletely recessive mutation? (Fitnesses are 1, 1 - h s, and 1 - s.)








5. Some rats with a particular allele have reduced susceptibility to the rodenticide warfarin. The alleles which confer this resistance also cause an increase in the rats’ need for vitamin K. In a particular population, the resistant homozygotes for the allele leave on average 1.95 offspring, heterozygotes leave on average 3.20 offspring, and the susceptible homozygotes leave 0.80 offspring. What would you expect the equilibrium allele frequency to be (assuming no mutation, migration, or drift)? If the allele frequency was 0.20 for the resistant allele in one generation, what would it be in the next generation?



6. A set of populations of cattle has been followed for several years and scored for the allele frequency of isocitrate dehydrogenase alleles. The frequency of this allele has not changed as much as we would have expected from drift given its total population size. Briefly discuss possible reasons for this observation.










7. What is the effective population size for a group of red deer which has 4 males and 35 females? Which would increase the effective size more, increasing the number of males or increasing the number of females?



8. The effective population size of a population of Drosophila in the lab is 120.

a. By what fraction will the genetic variance be reduced (assuming no mutation, migration or selection) after 3 generations? At equilibrium?







b. If the same population had a mutation rate to new alleles of 0.00001, what would the probability of identity of two randomly chosen alleles be at equilibrium? What would the homozygosity be in a population at Hardy-Weinberg equilibrium at that time?







9. Distinguish between:

a. Frequency-dependent selection and overdominance




b. Census and effective population size




c. Transition and transversion




d. Synonymous and non-synonymous mutations