Context: This passage describes the coat graying trait in horses:

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 having a graying coat (G) is dominant over the allele for not having a graying coat (g).
Dolly is a horse from this group. Dolly has the homozygous genotype gg for the coat graying gene.
Based on this information, what is Dolly's phenotype for the coat graying trait?
A. not having a graying coat
B. having a graying coat
Identify the correct option from the choices provided and respond with the letter of the correct option.
Answer: A