Large leopard frogs (Lithobates pipiens) outcompete smaller frogs for mates, but

Question

Large leopard frogs (Lithobates pipiens) outcompete smaller frogs for mates, but small leopard frogs are able to sneak some matings, undetected by the large males. Mid-sized males are too small to overpower the large males but too large to sneak matings. Accordingly, large males (AA) were assigned a relative fitness of 1; small males (aa), a relative fitness of 1-s_1; and mid-sized males (Aa) a relative fitness of 1-s_2. The selection coefficients s_1 and s_2 = 0.1 and 0.2, respectively. Assuming that initially p = 0.5, and q = 0.5, and all the conditions of the Hardy-Weinberg principle are met, what would be the relative contributions of each genotype to the next generation? Show your work. b) how many of each genotype would be expected in this next generation in a population of 1867 frogs? What kind of dominance is this? _____.

Explanation / Answer

Answer a:

wAA =1;     wAa = 1 – 0.2 = 0.8;     waa = 1 – 0.1 = 0.9;

Since Hardy-Weinberg principles are met, we have:

wbar = wAA p2+ wAa 2pq+ waa q2 = (1) (0.5)2 + (0.8) (2) (0.5) (0.5) + (0.9) (0.5)2 = 0.875

Adult genotype frequencies:

Freq(AA) = wAA p2 / wbar = (1) (0.5)2 / 0.875 = 0.2857

Freq(Aa) = wAa 2pq / wbar = (0.8) (2) (0.5) (0.5) / 0.875 = 0.4571

Freq(aa) = waa q2 / wbar = (0.9) (0.5)2 / 0.875 = 0.2571

Answer b:

Genotype to be expected in next generation in a population of 1867 frogs will be:

AA : 1867 X 0.2857 = 533 Aa : 1867 X 0.4571 = 854 aa : 1867 X 0.2571 = 480

Bonus Answer: Type of dominance - Complete dominance.

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