Question

how do you figure out "s" and "t" for balanced polymorphism?

p_E=t/(s+t)

q_E=s/(s+t)

Answer 1

answer) we can calculate the equillibrium frequencies in a balancing selection which is given as below:

genotypes: AA Aa aa

realtive fitness: 1-s 1 1-t

frequencies: p2 2pq q2

average relative fitness: w =p2 x(1-s)+ 2pqx1+q2(1-t)

so at p=0 you will get both equations

in this formulation, the terms 1-s and 1-t conations the selection cofficients that are ssumed to lie between 0 and 1. thus each homozygous has lower fitness than the heterozygotes. the superiority of heterozygotes is referred as overdominance.

in case of heterozygotes selection it tends to eleminate both a and A and favors Aa

so at balancing point A is p=t/(s+t) and frequency of a is q=s(s+t)

as an example let us suppose AA homozygous are lethal (s=1) and that the heterozygotes 50% fit (t=0.5)

p = 0.5/(0.5 + 1) = 1/3

q = 1/(0.5 + 1) = 2/3

nowboth the allels will mainnatin the appriciable frquencies and favors heterozygotes and this is known as the balanced polymorphism