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

MUTATION

• Mutations could lead to occurrence of new alleles and thereby it changes the gene pool of the population.
• It may be favourable or deleterious to the individual’s ability to survive.
• If changes are advantageous, then the new alleles will tend to prevail by being selected in the population.

• If a wild allele A ₁ mutates to A₂ with a frequency of u per generation.
• u is the proportion of all A₁ alleles that mutate to A₂ between one generation and the next.
• If the frequency of A₁ in one generation is p₀
• Then
  • The frequency of newly mutated gene A₂ in the next generation = u p₀
  • The new gene frequency of A₁ in the mutated population = p₀- u p₀
  • Therefore the change of gene frequency = – u p₀
• Suppose the gene mutates in both directions and the initial allele (gene) frequencies are p ( A₁ ), q ( A₂ )

• Then the change of gene frequency in one generation
  • Δ q = up - vq
• This situation leads to equilibrium in gene frequency at which no further change takes place. The point of equilibrium can be found by equating the change of frequency Δ q to zero.
  • pu – qv = 0
  • qv = pu
  • qv = (1-q)u
  • qv = u – qu
  • qv + qu = u
  • q(v+u)=u
  • q = u / (u + v)
  • Similary p = v / (v + u)
• If the mutational rates of A₁ to A₂ ( u ) and A₂ to A₁ ( v ) are known at equilibrium then the frequency of A₁ allele and A₂ allele can be calculated directly without using conventional method of estimating gene frequency