1) What is the difference between a stable equilibrium and a neutral equilibrium

Question

1) What is the difference between a stable equilibrium and a neutral equilibrium in population genetics (1)? What kind of data would you need to collect about a population to establish that it is in a stable equilibrium, as opposed to a neutral one (1)? Describe two different population genetic scenarios involving natural selection that are expected to cause a population to reach an equilibrium in allele frequencies (1). For each scenario, explain what population genetic mechanisms are operating, and what kind of equilibrium is obtained in each case and why (1). Give an example of one of the two scenarios (1).

2) Describe two different population genetic scenarios under which natural selection is not expected to achieve perfect adaptation (1). For each scenario, explain what population genetic mechanisms are operating (1.5), and how they lead to imperfect adaptation (1.5). Give an example of one of the two scenarios (1). (Note: do not use any of the examples given before Lecture #10 unless you do so in the context of an explicit population genetic scenario.)

3) Define the census size and the effective size of a population (1)? Describe two biological scenarios that may result in the effective size of a population being different from its census size (1.5). Explain in what way the two scenarios influence the effective population size (1.5). Give an example of one of the two scenarios (1).

4) Define (narrow sense) heritability (1). Why is it important for evolution (1)? Why is heritability the property of a specific population (1)? Describe one mechanism that can cause the estimated heritability of a trait to differ among populations, and how it works (2).

Explanation / Answer

1) (i) In a population, allelic frequencies can reach equilibrium due to mutation. A stable equilibrium is one which can reach its original equilibrium state after being disturbed. A neutral equilibrium remains at the allelic frequency that it has moved to when perturbed.

(ii) Data required to establish whether a population is in a stable state includes- a) population size, b) reproduction rate, c) mutation rate, d) rate of gene flow

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