Final answer:
The correct answer is (c) Grey; it is a dominant allele responsible for horses that are born a certain color and gradually become white or display white with black flecks as they age.
Step-by-step explanation:
A young horse with a Grey allele will be born any color but grey and will gradually become white or white with red or black flecks as it ages. The correct answer to the question is (c) Grey. This is a genetic trait that causes horses to undergo a progressive silvering of the coat, eventually leading to a white or flea-bitten appearance. The Grey allele is dominant over other coat color alleles, meaning that a horse only needs to inherit this allele from one parent to express the grey phenotype. Over time, a grey horse may develop black flecks scattered throughout the coat, which is particularly common in the flea-bitten grey variation.