用IBD型式计算乱伦案的似然比

Calculation of Likelihood Ratios for Incest Cases Using IBD Patterns

目的用血缘一致性(identity by descent,IBD)型式计算乱伦案件的似然比。方法先用相同的数字表示家系成员中IBD的等位基因以组成IBD型式,然后用先验概率乘以非IBD等位基因频率得出各个IBD型式概率。将家系的所有IBD型式概率相加即可得到乱伦案不同假设下的家系概率,比较不同家系概率计算似然比。结果获得了父女乱伦和全同胞乱伦案的IBD型式及这两种案例的似然比计算公式。结论阐明了基于IBD型式计算乱伦案似然比的方法。

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.