L15 Gene Flow cont

dn/ds = pin/pis

nutral evolution

dn/ds > pin/pis

positive selection

dn/ds < pin/pis

purifying selection

Cline

a change in trait mean or allele frequency over geographical space

Bergmann’s rule

groups of animals are larger in colder climates

Fst

genetic variance found across populations that results from genetic differences between them

isolation by distance

describes a pattern by which Fst increases as the distance between pairs of populations increases

local adaption

occurs when a population is differentially adapted to a specific geographic area

selection is increasing

genetic differences between populations

gene flow decreases

genetic differences between populations

How do allele frequencies evolve in different populations under selection and gene flow?

• depends on the relative strength of selection s and migration m

• p = 1 - m/s

s»m

allele will evolve primarily by selection

s « m

local adaptation will be overwhelmed by gene flow

gene swamping

a locally adapted allele could be lost entirely due to being overwhelmed by gene flow (p = 0)

Nem

average number of immigrants in each population in each generation

if Nem«1

the fst approaches one

if Nem>/= 1

Fst approaches 0