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Natural Selection

Explore the concepts of natural selection put forth by Darwin and Lamarck, including the passing on of acquired traits and the selection of individuals with advantageous combinations of traits. Learn about the synthetic theory of evolution and evidence supporting it such as the fossil record, comparative anatomy, biogeography, and subcellular studies. Discover the principles of microevolution, including the Hardy-Weinberg principle, mutation, selection, and genetic variation. Lastly, delve into the process of speciation through reproductive isolation.

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Natural Selection

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  1. Natural Selection

  2. Darwin vs Lamarck • Lamarck - animals pa on acquired traits • Darwin - individuals are selected for survival by combinations of traits • see page 303

  3. Darwin... • More individuals are born than live to reproduce • individuals vary from one another • individuals compete with each other for resources • individuals with the best combination of traits for the given conditions will survive

  4. What does natural selection not account for?

  5. Neo-Darwinism or Synthetic theory of evolution • Darwin posited that traits are passed on directly to the next generation • Mendel had already determined that traits are passed along as a matter of chance • the combination of Darwinian natural selection and Mendelian genetics is called the synthetic theory of evolution

  6. Evidence of evolution • Fossil record • Comparative anatomy (see Figure 7-17 on page 308) • Biogeography • subcellular

  7. Is the fossil record a complete record?

  8. Comparative anatomy • Homologous features- similar structure in different species • Analogous features - similar function different structure (convergent evolution) • Vestigial organs

  9. Biogeography • Evolution occurs only once • Center of origin • Related species have similar patterns of development (figure 17-12, page 313)

  10. Subcellular • DNA is universal • the longer the time since divergence the greater the difference in DNA

  11. Microevolution • Population = gene pool • Microevolution- small gradual changes within a population over time. Accounts for differences between population of same species

  12. Hardy-Weinberg Principle • This never occurs in nature but helps to understand the forces of evolution. • The frequency of genotypes in a population can be determined /described mathematically • Inheritance itself will not cause a change in allele frequencies

  13. Inheritance itself will not cause a change in allele frequencies • Allele frequencies will not occur if • there is random mating • there are no mutations • there is no migration • there is no natural selection • UNDER THESE CONDITIONS THERE IS GENETIC EQUILIBRIUM!!!!

  14. Mutation • A random, permanent change in DNA • does not determine the direction of evolution (mutations occur randomly, not in response to need or conditions) • Genetic drift - (founder effect) • Genetic bottleneck -

  15. Selection • Stabilizing selection - tends to make population more uniform • Directional stabilization - favors one extreme • Disruptive stabilization - favors both extremes • see page 327

  16. Variation • Genetic polymorphism - two or more alleles for a given gene. • What is the heterozygous advantage?

  17. Speciation • Species - members freely breed with one another • Reproductive isolation - • temporal isolation (different times) • behavioral isolation (courtship patterns) • mechanical isolation

  18. Speciation • Allopatric speciation - geographic separation results in new species • sympatric speciation - divergence in same geographic area (insects)

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