亲权指数计算的新方法

目的介绍一种亲权指数（paternity index,PI）计算的新方法。方法假定亲代的等位基因都要经过一个转变的过程才发生分离并遗传给子代。每个亲代的等位基因与子代相同时,其转变概率为1;当不相同时,其转变概率为0。且每个亲代的等位基因都有1/2的机会遗传给子代。据此,可以计算出孩子从争议父或母亲获得等位基因的概率。而随机男子提供等位基因给孩子的概率为等位基因频率。相应地算出PI值公式中的分子（X）和分母（Y）值。结果推导得到了一个能够计算三联体、二联体和失踪孩子案PI值的通用计算公式。结论本PI计算公式在亲子鉴定PI值计算上具有实用价值。

A New Method for Calculating Paternity Index

Objective To introduce a new method for calculating the paternity index（PI）. Methods Assuming that each allele from parents has undergone a transition before it segregates and transmits to child. The transition probability is 1 when parent allele is the same as child＇s, the transition probability is 0 when parent allele is different from the child＇s. Every allele has a transmission probability with 0.5. Base on these theories, it is easy to gain the probability that child inherits an allele from the alleged father or mother. Thus, the X value（numerator） and Y value（denominator） of PI formula can be calculated, as unknown man provide an allele for child with the allele frequency. Results A general formula that calculated the PI for trios, duos and missing child cases was deduced. Conclusion The new method is practical in all kinds of forensic paternity case.