Hardy weinberg

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Hardy weinberg

  1. 1. Population Genetics <ul><li>The Hardy-Weinberg principle </li></ul><ul><li>Factors that can change allele frequencies </li></ul>
  2. 2. A. The Hardy-Weinberg Principle <ul><li>The frequency of an allele in a population will remain constant over time, provided that the following conditions are met: </li></ul><ul><ul><li>The population is large and randomly breeding </li></ul></ul><ul><ul><li>There are no conditions acting on the population to change the allele frequency </li></ul></ul>
  3. 3. A. The Hardy-Weinberg Principle <ul><li>Consider a gene that has two alleles, A and a </li></ul><ul><li>Let p = the frequency of A (in a population) q = the frequency of a </li></ul><ul><li>The frequency of AA = p 2 The frequency of aa = q 2 The frequency of Aa = 2 pq p 2 + 2 pq + q 2 = 1 </li></ul>
  4. 4. Hardy-Weinberg Principle <ul><li>Population genetics - study of properties of genes in populations </li></ul><ul><ul><li>blending inheritance phenotypically intermediate (phenotypic inheritance) was widely accepted </li></ul></ul><ul><ul><ul><li>new genetic variants would quickly be diluted </li></ul></ul></ul>
  5. 5. Hardy-Weinberg Principle <ul><li>Hardy-Weinberg - original proportions of genotypes in a population will remain constant from generation to generation </li></ul><ul><ul><li>Sexual reproduction (meiosis and fertilization) alone will not change allelic (genotypic) proportions. </li></ul></ul>
  6. 6. Hardy-Weinberg Equilibrium Population of cats n=100 16 white and 84 black bb = white B_ = black Can we figure out the allelic frequencies of individuals BB and Bb?
  7. 7. Hardy-Weinberg Principle <ul><li>Necessary assumptions </li></ul><ul><ul><li>Allelic frequencies would remain constant if… </li></ul></ul><ul><ul><li>population size is very large </li></ul></ul><ul><ul><li>random mating </li></ul></ul><ul><ul><li>no mutation </li></ul></ul><ul><ul><li>no gene input from external sources </li></ul></ul><ul><ul><li>no selection occurring </li></ul></ul>
  8. 8. Hardy-Weinberg Principle <ul><li>Calculate genotype frequencies with a binomial expansion </li></ul><ul><li>(p+q) 2 = p 2 + 2pq + q 2 </li></ul><ul><li>p2 = individuals homozygous for first allele </li></ul><ul><li>2pq = individuals heterozygous for alleles </li></ul><ul><li>q2 = individuals homozygous for second allele </li></ul>
  9. 9. <ul><li>p 2 + 2pq + q 2 </li></ul><ul><li>and </li></ul><ul><li>p+q = 1 (always two alleles) </li></ul><ul><li>16 cats white = 16bb then ( q 2 = 0.16 ) </li></ul><ul><li>This we know we can see and count!!!!! </li></ul><ul><li>If p + q = 1 then we can calculate p from q 2 </li></ul><ul><li>Q = square root of q 2 = q √.16 q=0.4 </li></ul><ul><li>p + q = 1 then p = .6 (.6 +.4 = 1) </li></ul><ul><li>P 2 = .36 </li></ul><ul><li>All we need now are those that are heterozygous (2pq) (2 x .6 x .4)= 0.48 </li></ul><ul><li>.36 + .48 + .16 </li></ul>Hardy-Weinberg Principle
  10. 10. Hardy-Weinberg Equilibrium
  11. 11. B. Factors That Change Allele Frequencies <ul><li>Mutation </li></ul><ul><li>Migration </li></ul><ul><li>Natural selection </li></ul><ul><li>Random genetic drift </li></ul>

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