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Understanding Population Genetics: Allele Frequencies, Selection, and Mutation Dynamics

Population genetics is the study of allele frequencies within populations and the factors that influence their changes over time. Key processes include natural selection, where favorable traits enhance survival and reproduction, and genetic drift, where random sampling affects allele distribution. Additionally, mutation and gene flow from migration introduce new alleles. This knowledge is essential for predicting genetic variation and understanding evolutionary processes. We explore examples like moth coloration pre- and post-industrial revolution, illustrating these dynamics in real-world contexts.

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Understanding Population Genetics: Allele Frequencies, Selection, and Mutation Dynamics

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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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