Discussion on parentage index calculation of aborted fetuses with mixed STR typing
Objective In cases and events of mixed STR typing of aborted fetus,two methods for calculating paternity index(PI)of suspected biological fathers are proposed,which could be useful for theoretical reference for parental identification including mixed STR typing.Methods Depending on whether the fetal genotypes can be identified,the simple PI calculation method and the PI calculation method of deduced biological paternal genes when the fetal genotypes cannot be identified are proposed.Results The simple PI calculation method is to indentify the fetal genotypes first and then calculate according to the standard triplet.The PI calculation method of deduced biological paternal genes is to deduce all the possible genotypes of biological fathers conforming to Mendel's law(inference)without considering the ratio of peak height and peak area in mixed typing,and then calculate the parental index separately,taking the minimum value as the parental index of the locus.Conclusion When mixture ratio of fetus in the mixed typing of aborted tissue MR≥0.43,the accuracy of separation is very high and the simple PI calculation method can be accurate,so it is recommended.If 0.05≤MR＜0.43,it is suggested to use the calculation method of deduced biological paternal genes,which can avoid misjudgment of irrelevant persons to the greatest extent.If MR＜0.05,there's a high risk of fetal allele loss,we should not perform a paternity test on the mixed spot.Since the cumulative parental index calculated by deduced the biological paternal genes is usually lower than the value calculated by dividing the fetal genotype,the CPI may be lower than 10 000 when fewer loci are identified,and then more genetic markers should be detected.
Forensic geneticsShot tandem repeatMixed STR typingParentage indexMixture ratio
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NSTL
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