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Next time…

This overview explores the fundamental concepts of evolution, focusing on how populations, not individuals, evolve over time. Key factors contributing to evolutionary change include allele frequency, mutation, genetic drift, gene flow, and natural selection. By analyzing examples such as the adaptation of arctic foxes’ fur length to climate change, we illustrate the mechanisms of evolution and the importance of heritable traits in survival. The discussion emphasizes Darwin's observations and the role of selective pressures, including human influence through artificial selection.

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Next time…

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Presentation Transcript

  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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