Two of the genes that affect coat colour in horses are the extension gene and the cream dilution gene. The dominant E allele at the extension gene generates black coats, while the recessive e allele produces red coats. The coat colour caused by the extension gene is not altered if the horse is a homozygote for the C allele at the cream dilution gene. However, if the horse is a homozygote for the C^Cr allele at the cream dilution gene, it will have a white coat regardless of the extension genotype. This interaction between the extension and the cream dilution gene is an example of

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The interaction between the extension and the cream dilution gene is an example of epistasis, where the action of one gene masks or modifies the effect of another gene. In this case, the cream dilution gene modifies the expression of the extension gene, resulting in horses with the C^Cr allele having a white coat regardless of their extension genotype.

Two of the Genes That Affect Coat Colour in Horses