Lecture12_MigrationI - Gene flow and non-random mating I Gene flow(migration as an evolutionary force A Theory the one-island model One-way

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Unformatted text preview: Gene flow and non-random mating I. Gene flow (migration) as an evolutionary force A. Theory: the one-island model One-way movement of individuals (and alleles) from a large population on a continent to a Suppose that allele A1 is at frequency individuals Suppose that allele A2 is at frequency If on the island and that there are on the continent breeding individuals move from the continent to the island and begin to breed, the frequencies of the alleles in the island population are now: freq (A1): freq (A2): Upshot: B. What are the evolutionary consequences of gene flow? 1. Gene flow reduces differences between populations 2. May introduce new alleles; these may be II. Inbreeding as a form of non-random mating Inbreeding = mating among relatives A. When does inbreeding occur? 1. 2. 3. plant: humans: small populations B. What is the effect of inbreeding? Increases homozygosity = A1A1 A1A2 A2A2 NOTE: inbreeding does not change Therefore, inbreeding does not C. What is inbreeding depression? = inbred offspring have lower fitness than outbred offspring Mortality rate data in humans Group Young children (U.S.) Children < 20 (U.S.) Children < 10 (U.S.) At/before birth (France) Children (France) Children < 1 (Japan) Children 1-8 (Japan) Period Before 1858 1700s-1800s 1920-1956 1919-1950 1919-1950 1948-1954 1948-1954 Children of 1st cousins 22% 17% 8.1% 9.3% 14% 5.8% 4.6% Children of nonrelatives 2. Why does inbreeding depression occur? deleterious recessives are usually at so most occur in but inbreeding increases the proportion of therefore rapid ... it does not cause evolution, but it makes selection III. An introduction to sexual selection I. Sexual selection theory A. The observation: in some species, males and females Question #1: Why does this occur? B. Darwin's hypothesis: Sexual selection 1. Individuals experience differential success in 2. Variation in mating success is based on asexual species: survive and reproduce sexual species: Key point: Alleles that lead to increased success in Question #2: Why are males usually (not always!) the ones with elaborate traits used in courtship? Answer: sexual selection is usually much stronger in Why? Observation: In most species, females invest far more in Corollary 1: In females, reproductive success is limited by Corollary 2: In males, reproductive success is limited by Therefore, sexual selection on males is ...
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This note was uploaded on 04/10/2008 for the course BIOL 180 taught by Professor Freeman during the Fall '07 term at University of Washington.

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