Chapter 9 - Genetic Drift and Gene Flow

Notes for Understanding Evolution - Chapter 9

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Under Construction

Notes for Chapter 9: Genetic Drift and Gene Flow

Introduction

RQUE9.1: Why is genetic drift more likely to be important with smaller populations?

I. Role of Genetic Drift

RQUE9.2: In your own words, postulate a reasonable hypothesis to explain why the frequency of mottled versus striped phenotypes is so variable from population to population in Florida populations of the greenhouse frogs.

II. Theory of Genetic Drift

RQUE9.3: Repeat the calculations summarized in Table 9.1 (p. 101) for another hypothetical case of an introduced pair of frogs, together producing a pair of frog offspring, in this case with one of the founding frogs with genotype 'aa' (mottled phenotype) and the other frog with genotype 'Aa' (striped phenotype). What is the probability that both offspring (F1) are mottled phenotypes? Challenge: What is the probability that the second generation (F2) of two frogs will both be homozygous for the striped allele, considering any appropriate possibility for their two parents (F1)?

III. Founder Effect

RQUE9.4: Does the variation from population to population in striped versus mottled phenotypes of greenhouse frogs necessarily involve natural selection? Why or why not?

RQUE9.5: Contrast the drift versus selection hypotheses for explaining the absence of the B blood group in Native Americans, accepting the likely premise that the responsible allele was really quite common among their ancestors from Asia.

RQUE9.6: Compare the "cultural evolution" hypothesis for explaining why albinos are relatively common in Arizona Hopi tribes with a hypothesis that they are common due to genetic drift alone (see also p. 23).

IV. Religious Isolates

V. Amish of Pennsylvania

RQUE9.7: Extrapolate from the cases of the Dunkers and the Amish to what one might generally expect in a small population that is reproductively isolated from other members of the species.

VI. Consanguinity and Genetic Drift

RQUE9.8: Why do small human populations, like the one on Tristan da Cunha, tend to be inbred even if individuals only choose mates from other families?

VII. Gene Flow

IX. Caucasian Genes in African Americans

RQUE9.9: Reed's studies of the Duffy Factor suggest that African Americans in the U.S. today are, on average, not exclusively of African descent. Consider an alternative hypothesis for the higher incidence of the Duffy Factor in the U.S. and suggest a possible test to distinguish between the competing hypotheses.

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