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Evolution – change in allele frequencies within populations

Evolution – change in allele frequencies within populations. Population genetics – study of genetic structure of populations. allele frequencies. genotype frequencies. Population genetics. genotype frequencies allele frequencies. ✓. Describing genetic structure.

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Evolution – change in allele frequencies within populations

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  1. Evolution – change in allele frequencies within populations Population genetics – study of genetic structure of populations allele frequencies genotype frequencies

  2. Population genetics • genotype frequencies • allele frequencies ✓ Describing genetic structure • calculations • collecting data • patterns of genetic variation What can cause changes in allele frequency? • Hardy-Weinberg equilibrium • non-equilibrium conditions

  3. Allele and genotype frequencies genotype frequencies: allele frequencies: 200 white (rr) 500 pink (Rr) 300 red (RR) 200/1000 = 0.2 rr 500/1000 = 0.5 Rr 300/1000 = 0.3 RR 900/2000 = 0.45 r 1100/2000 = 0.55 R total = 1000 flowers

  4. 260 0.65 for a populationwith genotypes: calculate: Genotype frequencies Phenotype frequencies Allele frequencies 100/400 = 0.25 GG 160/400 = 0.40 Gg 140/400 = 0.35 gg 100 GG 160 Gg 140 gg 260/400 = 0.65 green 140/400 = 0.35 brown 360/800 = 0.45 G 440/800 = 0.55 g

  5. G G g g another way to calculateallele frequencies: Genotype frequencies Allele frequencies 0.25 GG 0.40 Gg 0.35 gg 0.25 100 GG 160 Gg 140 gg 0.40/2 = 0.20 0.40/2 = 0.20 0.35 360/800 = 0.45 G 440/800 = 0.55 g OR[0.25 + (0.40)/2] = 0.45 [0.35 + (0.40)/2] = 0.65

  6. How can we get information about genotypes and alleles in populations? • observe phenotypes • protein data (electrophoresis) • DNA data (electrophoresis or sequencing)

  7. How can we get information about genotypes and alleles in populations? • observe phenotypes • protein data (electrophoresis) • DNA data (electrophoresis or sequencing) Polymorphism – more than one allele at a locus How common is polymorphism?

  8. How genetically variable are populations? H0: little variation - because selection should remove less fit alleles - implies: mutations either good or bad, not neutral Ha: lots of variation

  9. Allele frequency variationwithin and between populations Frequency of Mdh-1 alleles in snail colonies in two city blocks

  10. Allele frequency variation in time Changes in frequency of allele F at the Lap locus in prairie vole populations over 20 generations

  11. How genetically variable are populations? H0: little variation - because selection should remove less fit alleles - implies: mutations either good or bad, not neutral Ha: lots of variation neutral theory – most mutations are neutral selectionist theory – variation in selection maintains different alleles in population - heterozygote advantage - fluctuating selection (selection varies in time or space) - frequency-dependent selection (rare allele is advantageous)

  12. Population genetics • genotype frequencies • allele frequencies ✓ Describing genetic structure • calculations • collecting data • patterns of genetic variation ✓ What can cause changes in allele frequency? • Hardy-Weinberg equilibrium • non-equilibrium conditions

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