In a certain species of parrot, having yellow feathers is a dominant trait and having green feathers is a recessive trait. A homozygous yellow parrot is crossed with a homozygous green parrot. If the female parrot lays four fertile eggs, what will be the phenotypes of the offspring?

If we label the yellow parrot alleles with YY (a homozygote) and green parrot gg (also a homozygote) we can cross these two individuals and determine their future offspring.

YY x gg

Yg Yg Yg Yg

All of the offspring would receive one dominant Y allele from the yellow parent and one recessive allele from the green parent and their genotypes would all be Yg (heterozygotes). Since Y allele is dominant, all of the offspring would have yellow feathers.