Lecture 38: Population genetics II
1. What possible explanations can be offered for loss of heterozygosity in certain populations found in the wild?
2. What criteria must be met for a genetic locus to be considered monomorphic? Polymorphic?
3. What is meant by the term "bottleneck" as it is used in genetics?
4. The Northern elephant seal has made a substantial recovery from near extinction. Why are geneticists still worried about its future?
5. Why is a high level of polymorphism in a population considered desirable?
6. What driving forces have caused the allelic frequency of HbS, which causes sickle cell anemia when it is homozygous, to become elevated in Central African populations?
7. What is the relationship between relative fitness and selection coefficient?
8. What is heterozygous advantage and what impact does it have on the population that emerges from an extended selective process?
9. In a population in which there is heterozygous advantage, what determines which of the two alleles that are involved reaches the highest equilibrium frequency? (You may have to make a common-sense extension from what has been presented to answer this one. Think in terms of the relative s values for the two homozygotes.).
10. Why does an allele that provides resistance to an adverse environmental condition not always become fully established and essentially monomorphic in a population?
11. Explain how a balance between selection and mutation can establish a constant allelic frequency for a recessive lethal trait.
12. Describe two different ways in which reduction of a population to a small size can permanently alter the genetic composition of the progeny of that population, even if their number later increases.
13. What are the mechanisms responsible for genetic drift, and how do they differ from founder effects?
14. Explain how an environmental change can alter selection. Illustrate with a real-life example.
15. Why is it valuable to have a high degree of heterozygosity in a population?
16. Explain why selection is not very effective in the complete removal from a population of an allele that is deleterious only when in the homozygous recessive state.
17. Explain how a disease epidemic can alter the balance of alleles that have nothing to do with resistance to that disease.
18. Explain how a pericentric inversion might give rise to disruptive selection, and how such selection might be the first step toward formation of separate species.
19. Describe a situation in which selection may not efficiently remove a dominant lethal allele from a population.
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