Calculation of Likelihood Ratios for Incest Cases Using IBD Patterns

Objective To calculate the likelihood ratios of incest cases using identity by descent （IBD） patterns. Methods The unique IBD pattern was formed by denoting the alleles from the members in a pedigree with a same digital. The probability of each IBD pattern was obtained by multiplying the prior probability by the frequency of non-IBD alleles. The pedigree likelihoods of incest cases under different hypotheses were obtained by summing all IBD pattern probabilities, and the likelihood ratio（LR） was calculated by comparing the likelihoods of different pedigrees. Results The IBD patterns and the formulae of calculating LR for father-daughter incest and brother-sister incest were obtained. Conclusion The calculations of LR for incest cases were illustrated based on IBD patterns.