= Solution
Only the copies inherited through the two related parents can share recent <identity by descent>; the other parental contributions come from unrelated <founders in a pedigree>. The related parents are <full siblings>. Their transmitted copies trace to the same shared grandparent with <probability> $1/2$, and then to the same copy of that grandparent with probability $1/2$. Thus the <first-cousin identity-by-descent probabilities> are
$$
\boxed{P(J=0)=\frac34,\qquad P(J=1)=\frac14,\qquad P(J=2)=0.}
$$
To compute the <kinship coefficient>, one random copy from each cousin selects those potentially shared contributions with probability $1/4$. Hence
$$
\boxed{\phi=\frac14P(J=1)+\frac12P(J=2)=\frac1{16}.}
$$
Back to article page
