FA2011lecture24

FA2011lecture24 - Explore two predictions arising from...

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Unformatted text preview: Explore two predictions arising from Darwin ` s concept of the origin of species: 1. All organisms are genetically related 2. Genes change gradually over time (random mutations); selection ensures l survival of the fittest z At the same time, learn about how genetics can be used as a tool to understand evolutionary change (holy grail: what are the genetic changes underlying the origin of new species?) For example, only 1% of human genes are unique to humans Degree of similarity (sequence conservation) varies among genes In general, the more closely related two organisms are thought to be (based on other criteria), the more similar their genes/proteins are For example, chimpanzee proteins are on average ~99% identical to human proteins (chimpanzee and human lineages diverged 5 MYA) Prediction 1: All organisms are genetically related Prediction 2: Genes change gradually over time (random mutations); selection ensures l survival of the fittest z Changes in DNA sequence occur randomly and constantly at rate= . Even without positive selection, some changes will become fixed due to genetic drift. Rate of neutral replacement = 2N X 1/(2N) = Number of new alleles in population of N individuals Probability of fixation in population of N individuals l Molecular clock hypothesis z : neutral changes should accumulate over time at a rate = , while deleterious changes should accumulate more slowly due to negative selection (no change...
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FA2011lecture24 - Explore two predictions arising from...

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