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Population Genetics & Evolution

Population Genetics & Evolution. Population Genetics & Evolution. Individuals do not evolve but populations do. Genetic Equilibrium. Occurs when the frequency of alleles remains the same over generations within a population. Genetic Equilibrium. Gene pool - All of the alleles of a

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Population Genetics & Evolution

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  1. Population Genetics & Evolution

  2. Population Genetics & Evolution • Individuals do not evolve but populations do

  3. Genetic Equilibrium • Occurs when the frequency of alleles remains the same over generations within a population

  4. Genetic Equilibrium • Gene pool - All of the alleles of a population’s genes

  5. Genetic Equilibrium • Allelic Frequency - percentage of a specific allele in the gene pool

  6. Genetic Equilibrium • A population that is in genetic equilibrium is NOT evolving

  7. Genetic Equilibrium • Anything that affects the genes in a gene pool can change allelic frequencies, which will disrupt a population’s genetic equilibrium and result in the process of evolution

  8. Mechanisms that disrupt a population’s genetic equilibrium • Mutations: introduce new alleles into the gene pool & change allelic frequencies

  9. Mechanisms that disrupt a population’s genetic equilibrium • Genetic drift - alteration of allelic frequencies by chance events • Occurs mainly in small populations that interbreed with each other

  10. Example of Genetic Drift • Allele for extra fingers & toes is 1 out of 14 in Amish people but 1 out of 1000 for the rest of the U.S. population

  11. Mechanisms that disrupt a population’s genetic equilibrium • Gene flow - transport of genes by migrating individuals Genes are lost from the gene pool when an individual leaves a population; genes are added when an individual enters a population

  12. Mechanisms that disrupt a population’s genetic equilibrium *The 3 mechanisms previously described primarily affect evolution of small, isolated gene pools (like those on islands) but their effect is often insignificant in larger, less isolated gene pools*

  13. Mechanisms that disrupt a population’s genetic equilibrium • Natural selection - the most significant factor that causes changes in established gene pools, whether they are large or small • There are 3 types of natural selection: stabilizing, directional, & disruptive

  14. Stabilizing Natural Selection • Favors the average individuals in a population • Reduces variation in a population

  15. Directional Natural Selection • Favors individuals with one of the extreme variations of a trait • Can result in rapid evolutionary change within a population

  16. Disruptive Natural Selection • Favors individuals with either extreme of a traits variation • Can lead to evolution of 2 distinct species

  17. The End

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