双方生母参与下半同胞关系鉴定中的似然比算法

Calculation of Likelihood Ratio for Identifying Half Sibling Relationship When Both Biological Mothers Participate

目的推导双方生母参与鉴定时半同胞关系似然比(likelihood ratio,LR)的计算公式。方法针对双方生母均参与下两个个体之间半同胞关系鉴定的情况建立半同胞关系甄别的检验假设,对备择假设与原假设条件下的遗传学证据的条件概率比值进行化简,并应用于一个半同胞关系鉴定的实际案例中。同时,在假设只有单方生母参与或双方生母均不参与的情形下,分别计算半同胞关系LR。结果在无生父参与的同父异母半同胞关系鉴定案件中,同样的遗传指标经检验分析后,双方生母参与下的累积LR值高于只有单方生母参与或双亲皆无情形下的累积LR值。结论用常染色体STR检验进行两个个体之间半同胞关系鉴定分析时,在双方生母均参与的情况下,其LR计算简单、直观、可操作性强。孩子生母应尽可能参与检验,否则需要增加检验STR基因座的数量才能获得更加明确的意见。

Objective To derive the formulae for likelihood ratio(LR) calculation of half sibling relationships when both mothers participate. Methods Based on the fact that both biological mothers participate in the identification of half sibling relationship between the two individuals, test hypothesis for the identification of half sibling relationship was established. Conditional probability ratios of genetic evidence under null hypothesis and alternative hypothesis conditions were simplified, and then applied to a real case of half sibling relationship identification. At the same time, the LR of half sibling relationships under the assumption that only a single biological mother or none of the biological mothers participate were respectively calculated. Results In the cases of identification of half sibling relationship from same fathers, with no biological father involved, after the same genetic indicator test analysis, when both biological mothers participate in the identification, the accumulated LR value was higher than that of accumulated LR with only a single biological mother or no parents participating. Conclusion When the autosome STR test is used for the identification and analysis of half sibling relationship between two individuals, the calculation of LR is more simple, intuitive and operable with both mothers participating. The biological mothers should participate in the test as much as possible, otherwise the number of STR loci would need to be increased for a more specific conclusion.