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Changing Allele Frequencies

Changing Allele Frequencies. Allelic Frequencies Change When There Is:. Non-random mating Gene flow/Migration Genetic drift Mutation Natural selection. Non-random Mating. We marry people similar to ourselves 80% of the time

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Changing Allele Frequencies

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  1. Changing Allele Frequencies

  2. Allelic Frequencies Change When There Is: • Non-random mating • Gene flow/Migration • Genetic drift • Mutation • Natural selection

  3. Non-random Mating • We marry people similar to ourselves 80% of the time • 1/3 of all marriages occur between people who were born <10 miles apart • Certain individuals contribute more to the next generation than others • Prize bull semen • Chinese immigrant to South African with rare dominant mutation that causes teeth to fall out by age 20 had 7 wives • Albinism in Hopi Indians • Genocide by rape in Darfur • Consanguinuity (a.k.a. inbreeding) • Endogamy =marriage within a community

  4. Non-random Mating

  5. Gene Flow/Migration • Individuals may join the migration • Individuals may mate within other populations along the way • Immigrants introduce alleles and emigrants remove them • A cline exists when neighboring populations have differing allelic frequencies • Geographical barriers (e.g. mountains) • Language barriers

  6. Gene Flow/Migration

  7. Genetic Drift • Chance sampling of alleles from the whole population • Due to: • Founder effect • Population bottleneck

  8. Founder Effect • Small group leaves the population to start a new settlement • New colony may have different allele frequencies than the original population • Ex: Small religious sect community in Utah/Arizona • Founded by 2 individuals in the 1930’s • 50% of all fumarate deficiency • Mental retardation, seizures, coma

  9. Population Bottleneck • Many members of a population die and only a few are left to re-populate • Much more restricted gene pool than original population • Ex: Pingalapese people of the East Caroline Islands in Micronesia • Typhoon wiped out all but 9 males and 10 females • Autosomal recessive achromatopsia very prevalent • Color-blindnesss, nearsightedness, and cataracts

  10. Genetic Drift

  11. Mutation • Major and continual source of genetic variation • One allele changes into another • Must occur in gamete in order to affect future generations and allele frequencies

  12. Genetic Load • Mutations that lead to lethal traits are often eliminated from the gene pool, however, some mutant alleles can persist in heterozygotes • Genetic load refers to the collection of these deleterious alleles in the population • Each of us has 5-10 recessive lethal alleles

  13. Mutation

  14. Natural Selection • Guided by changes in the environment • Individuals with certain phenotypes are more likely to survive and have reproductive success • Ex: Antibiotic resistance • Antibiotics select for those bacteria which are antibiotic-resistant

  15. Natural Selection

  16. Forces that Alter Allele Frequencies

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