Your genes define your starting point in life: nature versus nurture comes after, building on top. But as Carl Zimmer writes in the New York Times, the idea of this singular genetic “you,” that’s built up of cells carrying “your genes” is, upon closer inspection, kind of wooly. Especially if you’re a mother.
After a baby is born, it may leave some fetal cells behind in its mother’s body, where they can travel to different organs and be absorbed into those tissues. “It’s pretty likely that any woman who has been pregnant is a chimera,” Dr. Randolph said.
The genomes of your kids may be driving cells all over your body. In a study that analyzed the cells of women’s brains, says Zimmer, scientists “found neurons with Y chromosomes in 63 percent of them. The neurons likely developed from cells originating in their sons.”
But more than just collecting strange DNA from fetal cells, other people’s genomes can be picked up and incorporated into your own body. Twins can swap genomes in the womb, and organ transplant recipients can, in some sense, become their donor, with some of their cells carrying their donor’s DNA. Some people, says Zimmer, are even born with multiple genetic identities: “two fertilized eggs may fuse together” making one person with two genomes. One mother found out only after a medical test indicated that she was “not the mother of two of her three biological children,” Zimmer writes, ”that she had originated from two genomes. One genome gave rise to her blood and some of her eggs; other eggs carried a separate genome.”
More from Smithsonian.com: