(r = coefficient of) A measure of the probability that a gene in one individual will be identical by descent to a gene in a particular relative. An equivalent and alternative measure is the proportion of an individual's genome that is identical by descent with the relative's genome. Note that the genes must be identical by descent and not simply genes shared by the population as a whole. This means that r is the probability that the gene common to two individuals is descended from the same ancestral gene in a recent common relative.
Subjects: Zoology and Animal Sciences.