= Finite-population chromosomal coancestry
{title2=$\Phi_{G+1}=\Phi_G+\dfrac{1+F_G-2\Phi_{m,G}}{4(N-1)}$}
For $N$ individuals in monogamous families of exactly two offspring, let $\Phi_G$ be <mean> pairwise <kinship coefficient>, $F_G$ <mean> inbreeding and $\Phi_{m,G}$ <mean> kinship of mates. A random distinct offspring pair are siblings with <probability> $1/(N-1)$. Accounting separately for within-family and cross-family pairs gives the displayed recurrence, while $F_{G+1}=\Phi_{m,G}$. Random mating makes $\Phi_{m,G}=\Phi_G$. Sibling avoidance changes the mating-pair <mean>; it does not create unrelated founders or stop eventual drift to ancestral identity in a closed finite population.
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