Final answer:
If a horse has black hair on its points or an entire coat color, then the animal possesses an allele of the extension gene (Option E). The extension gene, symbolized as E, controls the production of black pigment. Understanding phenotypic ratios and gene interactions, such as those seen with the E gene in horses, is crucial in genetics.
Step-by-step explanation:
The correct gene associated with horses having black points or an entire black coat is the Extension gene, symbolized as E, which controls the production of black pigment.
Pinto, Dun, Roan, and Gray, as refer to different patterns and dilutions, not the base color.
Horses with at least one dominant E allele (EE or Ee) will display black pigment in their coat, while horses with the homozygous recessive genotype (ee) will not have black in their coat and will instead have a chestnut color.
Other genes, such as the Agouti gene, can further modify this pigment distribution, determining whether the black color is restricted to the horse's points or spread throughout the coat as a solid color.
In your question's context, which deals with inheritance patterns and gene interactions, it is important to recognize that a clear understanding of a basic phenotypic ratio and gene hierarchy is crucial.
For instance, in rabbits, multiple alleles exist for the coat color gene, and there's a certain hierarchy in which these alleles interact to produce the final color.
This concept is similar to how different alleles at the Extension locus interact with those at other loci to result in the varied coat colors seen in horses.
Hence, the correct answer is Option E. Extension.
The complete question is: If a horse has black hair on its points or an entire coat color, then the animal possesses an allele of the ____ gene.
a) Pinto
b) Dun
c) Roan
d) Gray
e) Extension