R = Coefficient of Relatedness

Synonyms

Calculating relatedness; Kinship; Measure of relatedness

Definition

A measure of the probability that two individuals share a gene due to recent, common ancestry.

Introduction

Relatedness is a consequence of individuals sharing copies of particular genes or alleles. Alleles are variants of the same gene, for example, one of the genes for eye color has an allele for blue eye color and an allele for brown eye color. The coefficient of relatedness, denoted by the symbol r, is a measure of the probability that two individuals share the same allele via a recent, common ancestor, and thus it is “identical by descent” (Hamilton 1964). This measure excludes any identical alleles that are shared simply by being members of the same population or species.

Calculating the Coefficient of Relatedness: r

In diploid species like humans, and most other mammals, an egg and sperm, each containing half the normal number of chromosomes, fuse to form a single cell or zygote; therefore, each parent...