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Evolution of Populations (Chapter 16)

Evolution of Populations (Chapter 16). Please set up your notebook for Cornell notes. Darwin Felt that variations in populations were important but did not understand how variations were passed from parent to offspring Darwin’s work was linked w/Mendel in 1930’s

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Evolution of Populations (Chapter 16)

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  1. Evolution of Populations (Chapter 16) Please set up your notebook for Cornell notes.

  2. Darwin • Felt that variations in populations were important but did not understand how variations were passed from parent to offspring • Darwin’s work was linked w/Mendel in 1930’s • Lead to discovery that natural selection works on genes in a population

  3. Genetic Variation • Gene pool  all the alleles and genes in a population • Frequency  the number of times a particular allele appears in a population • Evolution is an y change in the frequency of alleles in a population • Sources of genetic variation • Sexual reproduction  each parent passes on half of their genes so each offspring has a different combination of parental genes • Mutations  random changes in DNA; leads to a change in phenotype (physical appearance) • Mutations can be good or bad

  4. Single gene and polygenetic traits • Single gene trait  trait that has only two alleles • Widow’s peak  dominant trait • Polygenic trait  a trait that is controlled by two or more genes • Height in humans • Tends to be a bell shaped curve

  5. Evolution as genetic change • Natural selection doesn’t act on genes; rather is affects which individuals survive or die • Natural selection on single gene traits change gene frequency and lead to evolution

  6. Natural selection on polygenetic traits • Directional selection  when individuals on one end of the bell curve have higher fitness • Leads to phenotypes on one extreme • Stabilizing selection  individuals in the center of the curve have higher fitness • Leads to average phenotypes • Disruptive fitness  both extremes of the bell curve are selected for • Leads to phenotypes on both extremes of the curve

  7. Genetic Drift  a change in gene frequency due to chance • Founder effect  a population has a change in gene frequency as a result of migration • Leads to new species  speciation

  8. Speciation  usually occurs when a population becomes isolated • Reproductive isolation  two populations cannot interbreed and produce fertile offspring • Behavioral isolation  two populations could interbreed but courting behaviors keep them from breeding • Geographic isolation  two populations are kept apart by geographic barriers like rivers, mountains • Temporal isolation  two or more species breed at different times

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