DNA Curve Balls
Between innuendo and jocularities at a weekend BBQ, a fellow guest came upon the topic of sparsely documented DNA idiosyncrasies (not the testing, DNA itself). I was aware testing requires statistical prowess, making misinterpretation a real possibility - especially when the subject can’t afford good lawyers and expert witnesses to refute.
I was also aware that while DNA paternity tests can be used to identify the father for purposes of child support, a man who is paying support for the child of his lover’s affair often can’t use DNA proving he isn’t the father as grounds for discontinuing support. But again, that wrinkle is secondary to DNA itself.
Instead, I heard of a case where a birth mother’s DNA doesn’t match that of her own natural children! I had no idea this could happen. Apparently, it’s possible in rare (30 documented) cases of maternal chimerism, where two distinct DNA sets occupy different tissues in the mother’s body. Essentialy, a “twin lives microscopically inside the body as DNA.” If the mother passes on the minority DNA, the maternity tests can fail, seemingly, inexplicably.
Googling for this link led me to anther curiosity: twins/multiples with different fathers:
While extremely rare, it is possible for fraternal twins to have different biological fathers. This can occur if a mother ovulates twice in the same month, and each egg is fertilized by a different man’s sperm within that time frame. Identical twins, however, cannot be fathered by two different men because identical twins occur when one fertilized egg splits into two—the embryo contains DNA from only one sperm and one egg that split after fertilization and then multiply.
Naturally, I thought this was as rare as chimerism, alas: “scientists estimate that worldwide, one in 12 fraternal twin sets are bi-paternal, and science has named this type of twinning ‘hetero-paternal superfecundation.’”
Luckily, I’m not entangled in any DNA drama right now, but it still gives pause to know our perfect identifier has discontinuities. The perceived infallibility of the test adds to the burden of proof for exceptional subjects.