Britannica Sources used in this answer

Why is dominance variation difficult to use in selective breeding?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Red Poll cows — Animal breeding Red Poll cow and calf.

In the context of animal breeding, dominance variation is difficult to utilize because of the way one allele masks the effect of another at a specific genetic locus.1

When a dominant allele masks a recessive one, the resulting genotype of a heterozygous individual (carrying both alleles) cannot be outwardly distinguished from that of a homozygous individual (carrying two dominant alleles) based on their phenotype. Because breeders rely on observing an animal's physical traits to select for desired qualities, this inability to differentiate between these genotypes presents a major practical challenge in controlling and selecting for specific dominance effects.1

Unlike additive variation, where the effect of each allele contributes directly to the trait and can be more easily tracked and accumulated across generations, dominance variation remains complex to manage in selective breeding programs.1