Abstract:

A congenital chimera is an organism possessing two genetically distinct cell lines either in the whole body or limited to the haemopoietic tissues. This paper described two paternity cases in which blood samples from two externally normal alleged fathers showed abnormal STR profiles that more than two alleles were assigned at one locus. To clarify the chimeric form or origin and evaluate its consequence for forensic purpose, other tissue samples of the two alleged fathers, including hair follicles, buccal mucosa, semen and urine, as well as their family member's blood samples were additionally asked to be submitted. The autosomal STR profiles from all samples of both males revealed the presence of two maternal and paternal alleles at some loci, indicating they were “whole body chimera" derived from the fertilization of two maternal nuclei and paternal sperms. The chimeric male in case 1 might be form from the merging of male-female dizygotic twins due to paternal X alleles showing on his X-STR profile. whereas the other chimeric male in case 2 might be from the merging of male-male twins due to double maternal X alleles existing on his STR profile. Y -STR profiles of the both chimeric males showed normal and consistent with their male family members. Different allelic imbalances (<50-70%) were observed in different kinds of tissue samples.

Key words: chimerism , STR profile, forensic investigation

摘要：

先天性基因嵌合体由遗传获得，是胚胎早期两个不同受精卵相互混合或血管交叉吻合继而发育成的一个包含两套(种)不同细胞系的个体。分为血型嵌合体(twin chimeras)和全身器官组织嵌合体(whole body chimeras)两种。本文通 过两例亲权鉴定中发现的男性先天性嵌合体及其家族成员常染色体、性染色体的STR谱遗传分析，探讨先天性基因嵌 合体的类型、发生、基因嵌合现象在不同组织中的表现及其作为证据可能在法庭科学调查中存在的风险。分析结果表明， 两例男性Y-STR单倍型显示正常，分别与其男性家族成员Y-STR单倍型一致，但其在常染色体和X染色体上的STR基 因表现嵌合现象，分别是在胚胎发育早期由男性-女性、男性-男性的异卵双生子发生融合并发育而成的的全身器官组织嵌合体。嵌合体上不同来源组织的STR等位基因强度显示不均衡状态。

关键词: 嵌合体, STR分型, 法庭调查