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Population genetics

Population genetics. ANA215. Micro-evolution. Micro-evolution- change in allele frequencies between generations Allele frequency – proportion of one allele among all the alleles that occur at a given locus in a population. Factors: influence evolution. Mutation Migration/gene flow

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Population genetics

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  1. Population genetics ANA215

  2. Micro-evolution • Micro-evolution- change in allele frequencies between generations • Allele frequency – proportion of one allele among all the alleles that occur at a given locus in a population.

  3. Factors: influence evolution • Mutation • Migration/gene flow • Genetic drift • Natural selection • Lactose tolerance • Sickle cell anemia

  4. Human populations • Group of interbreeding individuals • Geography and culture • Endogamy • Inbreeding (non-random mating) • Exogamy • Breeding isolates

  5. Evolution • Allele frequency at a particular locus has changed from one generation to the next • Trait: tongue rolling (dominant)

  6. Hardy-Weinberg • Population is infinitely large • No mutation • No gene flow • Natural selection is not operating • Mating is random

  7. Observed calculations • Observed allele frequency • Observed genotype (number of individuals with a particular genotype) • Start with recessive alleles • p + q = 1

  8. Expected frequencies using Hardy-Weinberg • Expected genotypes (% of individuals ‘expected’ to have a particular genotype) • Expected number of individuals • Total number in the sample multiplied by the expected genotypic frequency • p2 + 2pq + q2 = 1

  9. Chi-squared test • Determine whether a statistically significant difference exists between the number of observed vs. expected individuals • Any value greater than 5.99 is statistically significant, which means evolution has occurred

  10. ABO blood group • Most populations are polymorphic for A, B and O. • Cline • Evolutionary significance is not known

  11. Rh system • Antigen found on red blood cells • Problems: Rh- mother/ Rh+fetus • 2nd pregnancy • Rh+ antibodies enter fetal blood: hemolytic diease

  12. MN blood system • No clinical complications • Three genotypes: MM, MN, and NN

  13. Biocultural evolution • Sickle cell anemia • Balanced polymorphism

  14. Biocultural evolution • Lactose intolerance • inability to digest milk/milk products

  15. Assignment • Hardy – Weinberg equations • Due: 24th April, 2005 • 50 marks/ forms part of your ANA 215 practical book

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