Chimerism-induced paternity confusion

Tetragametic chimerism occurs through the fusion of two zygotes formed by separate fertilization events, resulting in a single organism with intermingled cell lines. Tetragametic chimerism can manifest as a 50/50 split between cell lines, or with one cell line becoming the predominant set of DNA. The latter has been referred to as the main cell line “absorbing” the minor cell line.

A review of human chimeras compiled known cases of chimerism and their phenotypes, which include hermaphroditism, infertility, and multiple blood groups , among others. It is also possible for an individual to be unaware of their conditon if they do not display characteristic traits of chimerism.

In 2015, a case of in-vitro fertilization led to paternity confusion after a blood type discrepancy was discovered between the baby and the parents. Repeat paternity tests came back negative, however further microarray testing suggested a potential avuncular relationship. Later, it was determined that the father was a tetragametic chimera and the baby was conceived via sperm originating from the father’s “minor genome”. In clickbait terminology, the findings can be paraphrased as, “a man’s unborn twin was absorbed at birth AND fathered his child!”