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Next time…

Next time…. Read pp. 304-323. Evolution. Stepping back again Moving from individuals to populations Population – a group of organisms of the same species that live near one another and interbreed. Evolution. The genetic change in a population over time What’s changing? Allele frequency

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Next time…

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  1. Next time… • Read pp. 304-323

  2. Evolution • Stepping back again • Moving from individuals to populations • Population – a group of organisms of the same species that live near one another and interbreed.

  3. Evolution • The genetic change in a population over time • What’s changing? • Allele frequency • Examples…

  4. Evolution • Remember: • We measure traits • Evolution works on alleles • Think of allele frequencies, not individuals • Populations evolve, individuals DO NOT

  5. That Darwin Guy • Went out to the Galapagos • Saw a whole bunch of birds and other animals • Came up with the idea of evolution by natural selection • Wallace ALSO came up with evolution

  6. How it works • Example: arctic foxes and fur length • As climate changes, more storms • More extreme cold events • Long fur gives 20% better chance of survival

  7. Four ways that evolution happens • Mutation • Genetic drift • Gene flow/migration • Natural Selection

  8. Mutation • Ultimately the source of all genetic variation • Changes the DNA code • Alters the protein, which alters the phenotype for one or many traits • Usually deleterious, but CAN be beneficial

  9. Mutation • Mutation is the only way to get new alleles • Sex rearranges existing alleles into different combinations – shuffling the deck

  10. Genetic Drift • Random change: • Imagine a small population…

  11. Genetic Drift • Drift is affected by population size • Smaller populations have more extreme drift • Chance events balance more in large populations • Sometimes, an allele will go to fixation (become fixed)

  12. Drift • Two situations that cause severe drift: • The founder affect • A new population is started by a few individuals from the parent population • Population bottleneck • A non-selective event reduces the population size, alleles are lost

  13. Migration • Alleles move from one population to another • This changes the allele frequencies of BOTH populations

  14. Natural Selection • This is what we normally think of as evolution • Requires these three things: • Variation for a trait • The variation is heritable • The variation leads to differential reproductive success

  15. Natural Selection • Came from these observations: • More organisms are born than can survive • Some organisms are more likely to survive than others • Selective pressure

  16. Artificial selection • When the selective pressure is intentionally caused by humans • Crop plants • Domestic dogs • Etc…

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