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 lineages.

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!

Section C.

9. In Wales, the numbers of warfarin resistance genotypes of rat were as follows:

     Susceptible     Heterozygotes     Resistant

     Homozygotes                       Homozygotes

      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, p_eq = t/(s+t), to find the expected equilibrium frequency p_eq 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.