Evolution Final

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

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

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

no fitness difference (natural selection cannot act on the alleles, traits, etc)

• 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)

portion of the population that is reproducing

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

represents genealogical relationships within a population for a single locus

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)

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)

process of colonization from the populations nearest the previous range limits (i.e. plants/animals after ice ages)

probability of fixation is independent of population sizes (2s) for initial mutation

• selection dominates: s > 1/(2Ne) [Ne is effective population size]
• Drift dominates: s < 1/(2Ne) or s = 1/(2Ne)

change at molecular level (not phenotypic)--how DNA or RNA sequences and the amino acid sequences change over time

differences in amino acid sequence that do not manifest themselves in phenotypic differences

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

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)

• synonymous substitutions (same amino acid)
• non-synonymous substitutions w/ little effect on function (different amino acid)
• noncoding regions/pseudogenes
• effective neutrality (1>>2sNe)

many changes in protein-coiding DNA sequences do not cause changes in the amino acid sequence of the corresponding protein (synonymous subs)

• 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)

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

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)