A horse's coat color is primarily determined by what aspect of its genetics?

The primary genetic factor that determines a horse's coat color is the alleles, which are different versions of a gene that can exist at a specific location (locus) on a chromosome. Each horse inherits a combination of alleles from its parents, which interact in various ways to produce the horse's observable traits, including coat color.

Alleles can exhibit multiple patterns of inheritance such as codominance or incomplete dominance and can lead to a range of colors and patterns based on the specific genetic makeup of the horse. For example, one allele may code for bay coat color while another might represent chestnut, and the combination of these alleles will dictate the resulting coat appearance.

Other options, like environmental factors, influence a horse’s overall health and may affect aspects like coat glossiness and condition, but they do not fundamentally change genetic coat color. Lactation pertains to the feeding of young horses and has no role in defining coat color. Dominance is a genetic principle that plays a role in how certain alleles express themselves over others, but it does not encompass all factors determining coat color as alleles do. Therefore, alleles are the correct choice as they are the key genetic elements directly responsible for the variation seen in horse coat colors.