Question

Suppose a species has two generations per year, that adult survival rates of genotypes A1A1, A1A2, and A2A2 are identical, and that the fecundity values are 50, 55, and 70 in the spring generation and 70, 65, and 55 in the fall generation, respectively. Will polymorphism persist, or will one allele become fixed if fecundity values are unchanged for many years? What if the fecundity values are 55, 65, 75 in the spring and 75, 65, 55 in the fall?

Answer 1

Answer:

• Approximate absolute fitnesses (R) and relative fitnesses of these genotypes are:

Abslute fitness of A1A1 = 0.9 x 0.5 = 0.45

Abslute fitness of A1A2 = 0.85 x 0.55 = 0.4675

Abslute fitness of A2A2 = 0.75 x 0.70 = 0.525

Relative fitness of A1A1 = 0.45 / 0.525 = 0.857

Relative fitness of A1A2 = 0.467 / 0.525 = 0.889

Relative fitness of A2A2 = 0.525 / 0.525 = 1.0

• Selection coefficient = 1 – relative fitness

Selection coefficient of A1A1 = 0.143

Selection coefficient of A1A2 = 0.111

Selection coefficient of A2A2 = 0

Frequency of A2 = p = t / (s+t) ; t = generation; s =selection coefficient.

P = 1/ (0.143+1)= 0.87

Frequency of A1= q = 1 - 0.87 = 0.13

• Since the two generations a year and the fecundity just reverses, so the overall relative fitness remain the same, slowly the allele A2 will persist.

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