Abstract

Background: Nuclear genomic markers, like short tandem repeats (STR), are frequently employed for paternity verification and investigating crimes. As per Mendel’s law of inheritance, every living cell of an individual are expected to inherit identical DNA profile. However, extremely rare conditions such as chimerism or genetic mosaicism, arising from the fusion of two fraternal embryos in early development (Tetra gametic origin), make possible the shared existence of two genetically distinct cell populations within a single individual. Method: This paper explores a case study in which a foetus displayed both male and female genetic markers—one from the femur and another from blood— regardless of the same origin. Blood and femur bone exhibited chimerism at all twenty three informative autosomal loci tested, provided in Powerplex®-Fusion 6C PCR amplification kit (Promega). The existence of genetically male cell population in the chimeric foetus was confirmed by typing a Y-chromosome haplotype. Result: It would have been reasonable to assume that these samples came from two distinct individuals. However, after putting together data from different genetic researches and contextual information, the most plausible explanation suggested that the foetus was a chimera or a genetic mosaic due to the shared existence of two genetically distinct cell populations. Conclusion: This case underscores that chimerism may pose challenges for forensic analyses, as it can result in false paternity exclusions or render it futile to correlate the offender to a stain detected at a crime scene. Cautious data interpretation, an amended sampling plan, as well as efficient recognition of mosaics or chimeras, should enable avoiding such errors.

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