DNA Is Amazing And Kind Of Terrifying

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A Man’s Unborn Twin Fathered His Child Because DNA Is Amazing And Kind Of Terrifying

He didn't even know he'd absorbed his own twin until his baby has someone else's DNA.

When a couple who’d used artificial insemination to have a baby recently discovered that the father only shared 10% of his son’s DNA, they were afraid the fertility clinic had used the wrong man’s sperm.

Naturally they hired a lawyer, who suggested they consult a geneticist, and what they learned was incredible: The DNA belonged to the father’s unborn fraternal twin, which had been absorbed into his body while he was in his mother’s womb.

According to a report from Time, “It turned out that the DNA in the man’s sperm, which was 90% his DNA and 10% that of his twin’s, was from his unborn fraternal twin.”

The Time report went on to explain, “Vanishing twin syndrome, which refers to the condition in which one twin dies and is ’absorbed’ by the other, or by the mother or the placenta, occurs in anywhere from 20% to 30% of pregnancies with multiple babies. Apparently, the father had absorbed some of his twin’s cells in the womb, effectively becoming a blend, or chimera, of himself and his brother.”

This essentially makes the man’s genetic relationship to his own child more like that of an uncle.

According to Time, cases like this are rare, but not unheard of. They also noted that “Mothers retain some cells of their children, and a recent Danish study found that women who gave birth to boys retained cells with Y chromosomes. These can migrate throughout the body and have been found in the lungs, thyroid, muscle, blood, heart and even the brain of the mother.”

In this case, the absorbed twin’s cells remained in the man’s sperm — and probably elsewhere in his body, too.

Time reported that according to geneticist Barry Starr, who consulted with the couple, the man’s skin also showed signs of a striping pattern “because his skin cells are a chimera of the two as well—his twin’s skin tone was slightly darker and therefore shows up more distinctly against his lighter skin. His other tissues and organs are also likely a mix of the two DNAs, making matching for his blood type or other organs a challenge.”

The report also noted that chimerism, or the combining of two distinct sets of DNA, is what makes organ transplants work, and that the same is true “on a more sophisticated level with the new stem cell-based treatments that researchers are exploring now.”