Prof. Eernisse - Biol. 404
Review questions and challenges from 9/26/07 for Ch. 7, part 2, Freeman & Herron 4th Ed., posted by request
1. What molecular data surprised biologists in the 1960s and 1970s that ultimately led to the formulation of the "neutral theory" and "nearly neutral theory" of molecular evolution (as opposed to the then widespread "selectionist theory")?
2. If most accumulated molecular variation is neutral or only slightly deleterious mutations that get fixed in populations by genetic drift, rather than "positive selection" acting to favor mutations, then why are substitution rates observed to be similar in contrasting organisms with small or large population sizes? (Hint: Also contrast typical generation times for such organisms.)
3. As an example of how the neutral or nearly neutral theories have been extremely useful as a default assumption, explain how comparing the ratio of synonymous to nonsynonymous substitutions can reveal exceptional cases where positive selection is clearly acting at a particular locus.
4. Give examples for both within and between species comparisons where this has been demonstrated, and further generalize about the sorts of loci that are most clearly under positive selection.
5. Apart from replacement mutations, what is the evidence for both negative and positive selection acting also on silent (synonymous) mutations?
6. Elaborating on the last question, contrast "hitchhiking" ("selective sweep") and "background selection" as different mechanisms that could result in non-neutral silent substitutions.
7. Why does nonrandom mating, such as inbreeding, not lead to changes in allele (genotype) frequency but does lead to deviations in phenotype frequencies, compared with Hardy-Weinberg expectations?
8. If inbreeding is not expected to affect the evolution of populations, in terms of changes in allele frequency, why is it still considered an extremely important phenomenon that can affect evolutionary patterns within species?
9. What is inbreeding depression and how is it estimated? (Try to incorporate the conceptual tool, "coefficient of inbreeding" (F), in your response.)
10. Explain how researchers have implicated inbreeding depression as a likely factor involved in the recent decline of the greater prairie chicken, including tests that have been conducted as part of conservation genetics efforts to rescue the species from extinction.