In a population of chicken, three color morphs defined by two alleles occur: dark brown with genotype BB, light brown with genotype Bb, and white with genotype bb. A breeder takes only the light brown chickens for a new breeding group and then let the chickens select their partners. If purely positive assortative mating according to color morphs occurs in the breeding population of chickens, what would be the genotype frequency after many generations? Please explain your answer.