The nth of Jacquard’s (1970) nine condensed modes of IBD, described in Table 2

Without a subscript, is used to symbolize the coefficient of fraternity

A

The event A, typically the event of sampling some particular allele in some particular gamete

a

A random variable indicating whether event A occurred, which takes on a value of 1 when event A occurs, and a value of 0 when it does not

The probability of event A

The expectation, or mean, of the random variable a. Equivalent to P(A)

An estimate of

The nth central moment of a, defined as

A mixed central moment of a, b, and omitted variables, defined as

The inbred relatedness, which is the probability of sampling a locus where individual X is inbred and also related to individual Y

The coefficient of coancestry, or kinship, between individuals X and Y, which is the probability that an allele in individual X is IBD to an allele in individual Y. Also denoted by θ and in some texts

The second-order zygosity correlation of individuals X and Y, which is the probability that there are two pairs of alleles which are each IBD. Either both individuals are inbred but unrelated, or the individuals are genetically identical but not inbred

The fourth-order zygosity correlation of genotypes between individuals X and Y, which is the probability that all four alleles in the two individuals are IBD

The allele-frequency estimation error, the difference in allele frequencies between individuals X and Y

Quantitative-genetic terms

The additive genetic variation of the population

The dominance genetic variation of the population

The covariance of additive and dominance effects in inbred individuals

The variance of dominance effects in inbred individuals