University of London
(University College London)
BSc Degree 1996
GENETICS B7: POPULATION AND EVOLUTIONARY GENETICS
Answer ONE question from section A, TWO questions from section B, and ALL of section C (overleaf). Each section carries 1/3 of the marks on the paper.
Section A. Answer ONE of questions 1-3.
1. Review the importance of genetics to the understanding of evolution.
2. Are secondary sexual characteristics best explained by female choice for good genes or runaway models?
3. How do proponents of punctuated equilibrium differ from phyletic
gradualists in their interpretation of patterns of change in the fossil
record? Illustrate your account with reference to examples of particular
Section B. Answer TWO of questions 4-8.
4. What is the importance of gametic disequilibrium in evolution?
5. Is speciation a result of reinforcement of post-mating barriers?
6. Explain what is meant by an artificial selection experiment. Give two examples where this methodology has been successfully employed.
7. Large morphological changes can occur by a single mutation (such as a second pair of wings in mutant Drosophila): does this provide support for "hopeful monster" scenarios of evolutionary change based on macromutations?
8. Discuss what is meant by an evolutionary stable strategy (ESS). Give
details of the steps used in game theory analysis of animal contests and
describe a relevant example from a natural population.
Remember to answer Section C overleaf!
9. In Wales, the numbers of warfarin resistance genotypes of rat were
Susceptible Heterozygotes Resistant
Rw1/Rw1 Rw1/Rw2 Rw2/Rw2 Total
28 42 4 74
a) Estimate the allele frequencies at the Rw locus.
b) Find the expected numbers of genotypes given random mating.
c) Use a chi-square test to test whether there is any evidence for significant deviation from Hardy-Weinberg. Suggest three reasons why the genotypes might not be in Hardy-Weinberg equilibrium.
d) Use the values of O/E (observed nos. ÷ expected nos.) to estimate relative fitnesses of the three genotypes. Then standardize all the fitnesses to that of the heterozygote (Rw1/Rw2) by setting the relative fitness of Rw1/Rw2 equal to 1. What are these new relative fitnesses?
e) If the fitness of Rw1/Rw1 is 1-s, and the fitness of Rw2/Rw2 is 1-t, what are the values of s and t, the selection coefficients?
f) Now use the formula for equilibrium under heterozygous advantage, peq = t/(s+t), to find the expected equilibrium frequency peq of the Rw1 allele.
g) Assuming the deviation from Hardy-Weinberg is due to selection, will the equilibrium be stable or unstable? Briefly explain how warfarin resistance is expected to evolve.