A note on paternity computation in cases lacking a mother.

When the mother is unavailable for parentage testing, a calculation must usually be based on types determined for the child and the alleged father. Particularly in the case of DNA typing, the formula is easy to derive. The correct formula is apparently not widely known, however, and in fact, a formula that is obviously incorrect seems often to be used and quoted. The correct method of derivation is indicated, and formulae are given for the various possibilities for patterns of gene-sharing between child and alleged father. In most cases paternity = 1/4Pr(shared allele) is an adequate formula.