Question

A population of birds has two feather colours, white and black. Black is dominant over white. If you know that 75% of a population of birds totalling 4520 individuals has the dominant phenotype, determine how many individuals are heterozygous? Please show me the mathematical work to get to the answer!! :)

Answer 1

Heterozygous means that the bird(s) have the recessive and dominant genotypes. If you have 75% of a population of 4520 birds that have black feathers, that leaves 25% of the population to have white feathers. In order for 25% of the birds to have white feathers, the two genotypes must be Xx and Xx. This leaves the options for the following genotypes when using a punnet square (will add one at the bottom): XX, Xx, Xx, xx. This gives you the percentage of heterozygous birds, which is 50%. If you take 50% of 4520, (4520 x 1/2 = 2,260) that is the number of heterozygous birds in the population.
Final Answer: 2,260 birds are heterozygous.
Punnet Square:
     X    x
X  XX  Xx
x  Xx   xx