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Lecture21bio - BIOLOGY 1001 Friday April 4 2008 Lecture 21...

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BIOLOGY 1001 Friday, April 4, 2008 Lecture 21 Causes of Evolution: Gene Flow Movement of alleles from one population to another. Spreads beneficial alleles throughout a species. Maintains organisms over a large area as one species. Causes of Evolution: Genetic Drift Change in allele frequencies of a small population o Happens by chance o Reduces genetic variability within populations. o Increases genetic variability between populations. Population bottleneck Founder event Population Size & Genetic Drift Figure 15-2 Founder Events Increase Likelihood of Rare Alleles Small number of Amish founded population in PA. Ellis-can Creveld syndrome. Figure 15-4 Causes of Evolution: Non-random Mating Assortive mating – preference for mates that are similar to one’s self. Dominance – only a few dominant males have reproductive access. o Ex. Elephant seals, lions, elk, etc…. Sexual selection – one sex chooses mates based on certain traits.
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