Population Genetics and Evolution

  1. Hardy-Weinberg equilibrium
    in the absence of evolutionary forces, the frequencies of alleles and genotypes should remain stable or constant from one generation to the next; only if segregation and recombination occurs
  2. gene pool
    • the total number of alleles present in a population
    • because most animals are diploid, the population's gene pool is twice the number of individuals in that population
  3. p
    the frequency of the dominant allele
  4. q
    the frequency of the recessive allele
  5. the first Hardy-Weinberg equation
  6. the second Hardy-Weinberg equation
    p2 + 2pq + q2 = 1
  7. simplifying assumptions of the Hardy-Weinberg equilibrium:
    • the species is diploid
    • there are only two alleles involved
    • the species has discrete generations
    • the species is reproducing exclusively sexually (either monoecious or dioecious)
    • the trait under consideration is autosomal (not sex-linked, etc.)
  8. the five fundamental assumptions if the population is at equilibrium:
    • large (infinite) population size, thus no genetic drift
    • no mate selection (all mating should be random)
    • no net mutation
    • no net migration (the likelihood of either allele entering or leaving the population cannot differ)
    • no natural selection (one phentotype cannot be more successful)
    • * usually, one or more of these conditions are not met in natural or lab populations
  9. In general, the data does not support the ______ hypothesis.
  10. what can cause a change in the Hardy-Weinberg equilibrium:
    • mutation
    • random fluctuation in allele frequencies caused by small population size
    • gene flow
    • natural selection
    • mate selection (nonrandom mating)
  11. The processes of meiosis, fertilization, and random mating by themselves merely...
    ... expose alleles or allele combinations to evolutionary forces.
  12. the forces that cause evolution
    • mutation
    • population size
    • gene flow
    • nonrandom mating
    • natural selection
  13. mutation
    • is the original source of variation
    • an allele's advantages or disadvantages depend on the specific local environment; but are usually harmful
  14. mutant alleles can be carried along in populations in various ways:
    • masking my dominant genes
    • the gene locus being closely linked to other genes
    • the mutation has little effect on the fitness of the organism
  15. population size
    as populations get smaller, changes in gene frequencies can occur due to chance
  16. effects of small population size:
    • genetic drift
    • founder effect
    • bottleneck effect
  17. genetic drift
    • the random changes in gene frequencies through time
    • may lose an allele due to chance
    • not due to natural selection
  18. founder effect
    • a few individuals establish a new population
    • the genetic variation of the gene pool of the new population is very low
  19. bottleneck effect
    • when a large population becomes small, the population loses alleles
    • as a population increases, it is impovershed in genetic variation
    • a gene pool can begin to drift by chance after a population is drastically reduced by a disaster
  20. gene flow
    • occurs when genes are leaving or are introduced into a population as a result of individuals migrating in/out of a population
    • decreases variation between populations
    • absence of gene flow may lead to speciation
  21. nonrandom mating
    • occurs when individuals tend to mate with individuals that have the same or very different phenotypes (assortative mating and disassortative mating, respectively)
    • can affect the number of heterozygous (intermediate phenotypes) in the population
  22. natural selection
    • the differential survival and reproduction of phenotypes in the population
    • those with the adaptations that best enhances their chances of surviving and reproducting in that particular place and time (those organisms that are the most fit) tend to have more offspring
  23. three modes to natural selection are observed in nature:
    • stabilizing selection
    • directional selection
    • disruptive/diversifying selection
  24. stabilizing selection
    occurs when the average phenotype is favored over the extremes
  25. destabilizing selection
    • occurs when changes in the environment favors individuals with one extreme set of traits over that of the average phenotype
    • the average trait then shifts to that extreme trait
  26. disruptive/diversifying selection
    occurs when the selection is against the intermediate phenotype
  27. fitness
    the ability of an organisnm to survive and reproduce in a particular habitat at a particular time
  28. Speciation can occur when...
    ... the two populations diverge from each other tot he point that individuals from the two populations can no longer interbreed and produce fertile offspring.
  29. allozyme electrophoresis
    • obtain tissue samples from a number of individuals in a population
    • the proteins are separated using gel electrophoresis
    • a common method used to examine the allelic diversity in a population
Card Set
Population Genetics and Evolution
Unit 23