Migration models

Migration IN

Emigration Out Gene flow will homogenize allele frequency

Geographic Models Continent-island One way migration from large population to small population One way gene flow, [[genetic drift|founder effects]], small population size Island random migration between multiple populations random, physically separated stepping-stone A<->B<->C movement restricted to neighbors isolation-by-distance mating based on proximity, gene flow local, linear relationship between distance and genetic distance [[geographic variation|Ring species]]

Phylogenetic Models Isolation-by-migration Divergence with gene flow secondary contact secondary contact introgression Stable incorporation of alleles from one population or species into another after hybridization ghost introgression gene flow from an extinct or unsamples speciesi that leaves genetic traces, but no known population horizontal gene transfer gene move without reproduction across species boundaries Transformation- uptake of free DNE from the environment Transduction- gene transfer mediated by viruses Conjugation- direct cell-to-cell DNA transfer Endosymbiotic gene transfer- organelle -> nuclear genome

Measuring migration Number of migrants per generation Proportion of migrants per generation Fraction of ancestry/ admixture proportion Genome introgression measuring population subdivision $$ fixation index = Fst= (H_t-H_s) / H_t

$$ Hs= average heterozygosity, Ht= population heterozygosity Fst= 0: total mixing Fst= 1: total isolation High Fst = signature of [[genetic drift]] and/or [[selection]] acting differently across populations