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Population Genetics

Population Genetics. Population Genetics:. The study of allele frequencies within a population. Changes in allele frequencies are caused by the following: Natural Selection Genetic Drift Mutation Gene Flow. Natural Selection.

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Population Genetics

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  1. Population Genetics

  2. Population Genetics: • The study of allele frequencies within a population. • Changes in allele frequencies are caused by the following: • Natural Selection • Genetic Drift • Mutation • Gene Flow

  3. Natural Selection A process whereby creatures with good traits survive and reproduce and where creatures with negative traits, die off.

  4. Genetic Drift • Changes in allele frequencies due to the fact that alleles in offspring are a random sample of those in parents. • Not a result of which traits are beneficial, genetic drift is random.

  5. Causes of Mutation Spontaneous Radiation Chemicals/pollution Crossing over during meiosis Meiosis makes sperm and egg

  6. Gene Flow • Transfer of alleles from one population to another. • Caused by the migration of organisms

  7. Genetics • Let’s say “B” = Brown and “bb” = white. • Geneticists can predict babies • Bb x bb = 50% Brown and 50% White

  8. Genetics • Let’s say “B” = Brown and “bb” = white. • Let’s say that 4% of a population is white. • Geneticists can now predict for the population 4% = 0.04 “bb”= 0.04 “b” x “b” = 0.04 The square root of 0.04 = 0.2 “b” = 0.2 Therefore “b” = 20% of all alleles B b = 0.2 4% of the population B BB Bb 4% b = 0.2 bB bb

  9. Genetics • If “b” = 20% of all alleles, then… • “B” must equal 80%. B = 0.8 b = 0.2 4% of the population B = 0.8 BB Bb 4% b = 0.2 bB bb

  10. What percent of the bunny population will be homozygous dominant? B = 0.8 b = 0.2 64% 16% B = 0.8 BB Bb 16% 4% b = 0.2 4% of the population bB bb 64% will be BB. 32% will be hybrids

  11. A new recessive mutation has resulted in 9% of the USA becoming vampires. What percent of the population will be carriers? N = 0.7 n = 0.3 49% 21% N = 0.7 21% 9% n = 0.3 42% will be carriers.

  12. “b” = 0.6. Do the rest. B = 0.4 b = 0.6 16% 24% B = 0.4 24% 36% b = 0.6 What are the percentages of the different genotypes? Fill out the punnett.

  13. No mutation: no allelic changes occur. No gene flow: Animals do not enter or leave the population. Random mating: individuals pair by chance and not according to the genotypes or phenotypes. Large population: the population is large so changes in allele frequencies due to chance are insignificant. Large populations decrease chances of genetic drift. No selection: All genotypes are healthy and there is no selective force that favors one genotype over another.

  14. Within a population of moths, the color dark (D) is dominant over the color white (d). Before the industrial revolution, nearly 81% of all moths were white. What percentage of the population was DD before the environment was polluted? D = 0.1 d = 0.9 1% 9% D = 0.1 dd 9% 81% D _ d = 0.9 1% of the butterflies will be DD.

  15. Mutations occur Gene Flow. Animals enter or leave the population, thereby introducing or eliminating alleles. Non-random mating. Animals breed according to phenotypes or genotypes. Small population Selection. One genotype is selected over another. Which moth was selected for during the industrial revolution?

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