This passage describes the coat graying trait in horses:
Your hair may turn gray or white as you grow older. Some horses go through a similar process called coat graying as they age. These horses are usually a darker color, such as brown or black, when they are born. Over time, the hairs of their coats lose their original color and become gray or white.
In a group of horses, some individuals have coat graying and others do not. In this group, the gene for the coat graying trait has two alleles. The allele for not having a graying coat (g) is recessive to the allele for having a graying coat (G).
The Punnett square below shows a cross between two horses. Consider the genotypes of the offspring shown. Select all the boxes that represent offspring with a homozygous genotype.