inbreeding, mutation, migration, drift

inbreeding

form of non-random mating

identical by descent

alleles at a locus are copies of an allele present in an ancestor, probability of occurring is increased by inbreeding

inbreeding coefficient (F)

overall probability that the two alleles inherited by a given individual will be identical by descent

changes in genotype frequencies due to inbreeding

• more heterozygotes

  • f(AA) = p² + Fpq

  • f(aa) = q² + Fpq

• fewer heterozygotes

  • f(Aa) = 2pq(1-F)

inbreeding depression

• reduction in the viability of inbred individuals

• occurs because more deleterious conditions are recessive and require two copies of the mutation to be expressed

evolutionary forces that change allele frequencies

• mutation

• migration

• genetic drift

• natural selection

mutation

• ultimate source of genetic variation

• occurs rarely at a single locus and thus does not alter allele or genotype frequencies rapidly

migration

• can be frequent or infrequent

• when frequent and non-directional, it tends to homogenize the allele and genotype frequencies of separate populations

• can be maladaptive

genetic drift

• moves allele frequencies up or down with equal probability (random)

• strongest in small populations

bottleneck

population is greatly reduced in size, limiting the genetic variation of the species

founder effect

loss of genetic variation when a new population is established by a very small number of individuals from a larger population (small group carries only a fraction of the original population’s genetic variation)