Breeding Value

A breeding value is the additive genetic contribution of an individual to the phenotype of its offspring. In quantitative genetics, it is the portion of an individual's genotype that can be passed on and selected for, as opposed to dominance effects or epistatic interactions that do not breed true. The breeding value is not an observed quantity; it is estimated from pedigree records, phenotypic measurements, or genomic markers.

The concept was formalized by Ronald Fisher as part of the 1918 synthesis that unified Mendelian inheritance with biometrics. Fisher showed that the correlation between relatives could be decomposed into additive, dominance, and environmental components, and that selection operates primarily on the additive component — the breeding value.

Modern genomic selection uses dense marker panels to estimate breeding values without traditional pedigree information. This has revolutionized livestock breeding and is increasingly applied in crop improvement. But the underlying assumption — that additive gene action captures the heritable variation — remains as contested today as it was in Fisher's time, because gene-environment interaction and epistasis routinely violate it.