Evolution Final

Card Set Information

Evolution Final
2011-05-28 21:05:48

Final Review
Show Answers:

  1. Law of Large Numbers
    as the size of a random sample increases, the realized frequencies (those observed) will be very close to the expected frequencies--when the sample sizes are small, the realized frequencies with not always be close to the expected frequencies
  2. Wright-Fisher Model
    for small populations--assumes: 1. natural selection is not acting on trait 2. Mating is random w.r.t locus 3. No mutations 4. no migration into the population
  3. Genetic Drift
    process of random fluctuation in allele frequencies due to sampling effects in finite populations Three consequences: 1. allele freq fluctuate over time 2. heterozygotes decrease by 1/2N each generation 3. separate populations diverge in allele freq
  4. Selectively neutral
    no fitness difference (natural selection cannot act on the alleles, traits, etc)
  5. Observed vs. Expected Heterozygosity
    • Observed: fraction of individuals that are heterozygous at a given locus (one minus the freq of homozygotes)
    • Expected: fraction of heterozygotes expected under HW equilibrium given allele freq of population (one minus p^2 and q^2)
  6. Effective Population Size
    portion of the population that is reproducing
  7. Coalescent Theory
    how gene copies spread through a finite population over generations using gene trees--trace the ancestry of the gene copies backward in time until they coalesce (at the coalescent point)--small populations take less time to coalesce than large populations
  8. Gene Trees
    represents genealogical relationships within a population for a single locus
  9. Population Bottleneck
    a brief period of a small population size--increases rate of genetic drift (alleles fluctuate, reduces heterozygosity by 1/2N (allele fixation), divergence between population)
  10. Founder Effect
    refers to the change in allele frequencies that results from sampling effects that occur when small isolated populations initially colonize a new area and found a new population (increases rate of genetic drift on new population)
  11. Leading Edge Expansion
    process of colonization from the populations nearest the previous range limits (i.e. plants/animals after ice ages)
  12. Haldane's Model
    probability of fixation is independent of population sizes (2s) for initial mutation
  13. Kimura's model
    • selection dominates: s > 1/(2Ne) [Ne is effective population size]
    • Drift dominates: s < 1/(2Ne) or s = 1/(2Ne)
  14. Molecular Evolution
    change at molecular level (not phenotypic)--how DNA or RNA sequences and the amino acid sequences change over time
  15. Cryptic molecular variation
    differences in amino acid sequence that do not manifest themselves in phenotypic differences
  16. Neutral Theory (of molecular evolution)
    at the molecular level of DNA or amino acid sequence: 1. most of the variation present within a population is selectively neutral 2. Most of the changes in DNA or amino acids sequence over time are selectively neutral--selection isn't acting so drift is responsible for DNA sequence changes over time; most substitutions are neutral, not most mutations
  17. Substitution
    occurs when a new allele arises by mutation and is subsequently fixed in the population--the substitution rate is the rate at which new alleles become fixed in populations (substitutions/generation)
  18. Reasons for selective neutrality
    • synonymous substitutions (same amino acid)
    • non-synonymous substitutions w/ little effect on function (different amino acid)
    • noncoding regions/pseudogenes
    • effective neutrality (1>>2sNe)
  19. Degeneracy of Genetic Code
    many changes in protein-coiding DNA sequences do not cause changes in the amino acid sequence of the corresponding protein (synonymous subs)
  20. Molecular Clock
    • substitution rates at neutral loci do not depend on population size or other demographic parameters, so proponents of the neutral theory suggest that selectively neutral mutations arise at similar rates in different taxa
    • Substitution rate = kv (k: number of neutral loci, v: mutation rate for each of the loci)
  21. Genetic Equidistance
    if molecular evolution proceeds at the same constant rate over time in different lineages, all members of a clade should be genetically equidistant from an outgroup (distance is measured at the number of DNA or amino acid sequence difference)--breaks down when evolution occurs at diff rates
  22. Nearly Neutral Theory
    most substitutions are, if not exactly neutral, only mildly deleterious--selection and drift act, and population size matters--generation time is highly correlated with population size, so species with larger populations tend to have shorter generation times (factors cancel so rate of synonymous subs is constant per year)