Male birds of the species Parus major express one of two different shades of yellow in their breast feathers. Some males have bright yellow breast feathers, and other males have pale yellow breast feathers. Males with pale breast feathers produce sperm that are less mobile than sperm produced by males with bright breast feathers. Females prefer to mate with mafes that have bright yellow breast feathers.

Which of the following rows identifies a factor influenced by the expression of two types of breast feathers of male birds and describes the potential effect of the factor on the population's gene pool?
factor effect of factor
a. non-random mating disrupts genetic equilibrium
b. the bottleneck effect maintains genetic equilibrium
c. non-random mating maintains genetic equilibrium
d. the bottleneck effect disrupts genetic equilibrium