Expectations from a
Punnet square for individuals vs populations
A cross between two heterozygous individuals A1A2 produces an expected ratio of 1 : 2 : 1 :: A1A1 : A1A2 : A2A2. Random mating in a population with allelic proportions f(A1) = p and f(A2) = q produces an expected ratio of p2 : 2pq : q2 :: A1A1 : A1A2 : A2A2. If p = q = 0.5, the population Punnet square resembles that for an individual cross, with expected offspring ratios 0.25 : 0.50 : 0.25, that is, 1 : 2: 1. For any other value of q, the proportions of the sides of the square lead naturally to the areas of the four boxes.