AGB 121: Principles of Animal Genetics and Population Genetics (2+1)

MIGRATION

• Migration is the movement of individuals from one breeding population to another.
  • Immigration is the inward migration of individuals into a population from other populations.
  • Emigration is the outward migration of individuals from a population. This brings about the reduction in the size of the gene pool.
• The migration of breeding animals to or from a population can cause changes in gene frequency.

• Let us suppose that a large population consists of a proportion of “m” of new immigrants in one generation then the remainder (1-m) being natives.
  • Number of natives = n₁
  • Number of immigrants = n₂

• Let the frequency of a certain allele ( A ) be q_m among the immigrants and q₀ among the natives.
• Then the frequency of the allele in the mixed population q₁ will be

q₁ = m q_m + (1 – m) q₀

q₁ = m q_m + q₀ – m q₀

q₁ = m q_m – m q₀ + q₀

q₁ = m (q_m – q₀) + q₀

• The gene frequency in mixed population will depend on the original gene frequency of the population and the difference in gene frequency between the immigrants and native (q_m – q₀) and the proportion of immigrants.
• The change of gene frequency Δq brought about by one generation of immigration is the difference between the frequency before immigration and the frequency after immigration.

Δ q = q₁ – q₀

Δ q = m (q_m – q₀) + q₀ – q₀

Δ q = m (q_m – q₀)

• Thus the rate of change of gene frequency in a population subject to immigration depends on the immigration rate and the difference in gene frequency between the immigrants and the natives.