BIOL 121 Lecture : Biol 121- 2010.03.24- Evolution- Speciation (Ch. 26).docx

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11 Dec 2012
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BIOL 121 Full Course Notes
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Speciation creates evolutionarily independent populations (e. g. ground finch) Barriers that prevent reproduction (ie. prevent gene flow) (2 main types) Mutation and genetic drift cause change in allele fq. Gene flow between populations keeps allele fq constant. If gene flow stops, the populations will diverge and at some point, divergence is significant enough that speciation occurs. When gene flow ends, allele fq in the isolated populations are free to diverge and evolve independently. If mutation, selection, and genetic drift cause isolated populations to diverge sufficiently, distinct types, or species form speciation. Large ground finch and medium ground finch are derived from same ancestral population. This ancestral population is split into two populations isolated by the lack of gene flow (occupying different islands once the ancestral population splits into separate populations) Because populations began evolving independently, they acquired the distinctive characteristics observed today. The two main types of barriers that prevent reproduction or prevent gene flow are prezygotic barriers and postzygotic barriers.

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