Migration is the movement of individuals from one population into another population and where the individuals joining a population contribute alleles to the subsequent generation(s) in that population.
If migration occurs from population 2 into population 1, the potential parents in population 1 are now comprised of some frequency of individuals from population 2 ($m$) and the remaining frequency of individuals from population 1 that existed before the migration occurred ($1 - m$).
|Generation 0 (before migration)||Population 1||Population 2|
|Frequency of A allele||0.35||0.70|
|Frequency of a allele||0.65||0.30|
Assume that migration occurred at the rate of m = 0.20 from population 2 to population 1 (20% of the parents to produce the subsequent progeny generation in population 1 came from population 2).