Ch. 20

• Population

  Group of individuals with common set of genes that live in same geographical area (actively and potentially interbreed)
• Gene pool

  The total genetic information in a population
• Rules and laws for Hardy-Weinberg Equilibrium (HWE)

  • Population size= infinite
  • Random mating (genotype frequencies guessed by allele frequencies)
  • No natural selection
  • No migration (no gene flow)
  • Mutation doesn't introduce new alleles
  • Genetic drift does not occur
• HWE predicts stable allele frequencies, predictable genotype distribution, stable equilibrium frequencies, predictable effects of random mating
• HWE calculations


  p+q=1

  p^2 + 2pq + q^2 = 1
• CD4


  Docking station for HIV
• CCR5


  Interacts with CD4 and dissolves cell membrane
• In late stage infections HIV uses CXCR4
• Fitness


  An individual's genetic contribution to the next generation; relative fitness= w; w=1 with highest reproductive success; w=0 when individual dies before producing offspring
• Selection of an allele

  Interacts with frequency of deleterious alleles and fitness
• Types of natural selection

  • Stabilizing: preserves average phenotype
  • Directional: favors individuals on one of the extremes
  • Disruptive: favors individuals on both extremes (against those in the average); increased variation, two distinct populations
• Mutation alone acts to create new alleles and changes allele frequencies
• Gene flow (migration)


  Movement of alleles from one population to another (new alleles, increased/decreased present alleles)
• Immigration


  Movement into a population
• Emigration


  Movement out of a population
• Genetic drift


  Random changes in allele frequencies
• Effects of genetic drift

  • Founder Effect: population originates from small group
  • Bottleneck effect: environmental conditions result in survival of only a few individuals
• Populations that underwent a population bottleneck

  • Cheetahs
  • Buffalo
• Types of nonrandom mating

  • Positive assorted mating: similar genotypes are more likely to mate
  • Negative assorted mating: dissimilar genotypes are more likely to mate
• Degrees of relatedness


  • First-degree: parents and children, share 50% alleles
  • Second-degree: sibling, grandparents, and grandchildren, share 25%
  • Third-degree: uncle, aunts, and first cousins, 12.5%
• Inbreeding


  Mating between related individuals
• Inbreeding depression


  Lowered mean fitness in inbred populations
• Models of Hominin Evolution

  • Multiregional Hypothesis (MRE)
  • Recent African Origin (RAO)
• Rare alleles have a population frequency less than or equal to 1%
• Some alleles are "private" to an individual, family or population
• Nuclear diversity studies using SNPs were not used to support the RAO model, Mitochondrial DNA was used to support RAO model
• Autosomal genetic diversity is greater in African populations than in non-African populations
• Ancestral allele


  Shared by humans and gorilla but not chimp
• Derived allele


  Differ from those that are from gorillas and chimps
• Interbreeding occurred for Denisovans and Neandertals in East Asia, Western Europe, and Australia New Guinea with modern humans