Kinship and Inbreeding

Abstract

The kinship coefficient quantifies the genetic similarity between two individuals by the probability that randomly sampled homologous genes from the two individuals are identical by descent (IBD) given their pedigree‐based relationship. Inbreeding is the probability that the two genes at a locus are IBD. These probabilities played a key role in modelling genetic covariances between relatives, which provided the theoretical foundation for the quantitative genetic analyses of polygenic traits. At present, genotypes are becoming available at the trait loci or at the loci closely linked to them. Given such genotypic information, analyses that are based on genetic covariances between relatives conditional on pedigree are becoming obsolete together with pedigree‐based coefficients of kinship and inbreeding. Key Concepts Before the availability of genotype information, covariance between relatives conditional on pedigree information provided the theoretical foundation for the quantitative analyses of polygenic traits. Kinship and inbreeding coefficients played a key role in modelling genetic covariances between relatives. Analyses that are conditional on genotypes are more informative than those conditional on pedigrees. Pedigree‐based analyses are being replaced by genotype‐based analyses.