Genetic diversity is often a major consideration in e g forest crops.
The probability that the first gene originates from genotype i in the seed orchard is pi, and the probability that the second originates from genotype j is pj.
The probability that these two genes originate from the orchard genotypes i and j are identical by descent (IBD) is θij.
This is the Malecot's method of coancestry[1] (or "coefficient of kinship"; "coefficient of relationship" is a similar measure which can be computed) between genotype i and j.
The formula for the group coancestry (from which gene diversity can be obtained) of seed orchard crops is:[2]
The group coancestry of a seed orchard crop can be divided in two terms, one for self-coancestry and one for cross-coancestry: