Girls sometimes inherit almost two full sets of their dad's genes


Originally published at:


That dad has taken mansplaining to a new level.


Another entry in the “genetics is weird” category:

Ranchers are familiar with one type of chimera, the freemartin, which results when a cow carries opposite-sex twins… Zimmer describes a bizarre twist on the free-martin: a girl with different-colored eyes and ambiguous genitals who appeared at a Seattle genetics clinic. Her ovaries proved to have only XX chromosomes—typical female—but her other tissues were mixtures of XX and XY. Further analysis showed that she had started out as opposite-sex twins. But early in development, the two embryos had fused, becoming a single, highly unusual child. Like a verse from the old Ray Stevens novelty song “I’m My Own Grandpa,” this girl was her own twin brother.

In pregnant women, fetal stem cells can cross the placenta to enter the mother’s bloodstream, where they may persist for years. If Mom gets pregnant again, the stem cells of her firstborn, still circulating in her blood, can cross the placenta in the other direction, commingling with those of the younger sibling. Heredity can thus flow “upstream,” from child to parent—and then over and down to future siblings.

Every one of us carries a unique flora of hundreds if not thousands of microbes, each with its own genome, without which we cannot feel healthy—cannot be “us.” These too can be passed down from parent to child—but may also move from child to adult, child to child, stranger to stranger. Always a willing volunteer, Zimmer allowed a researcher to sample the microbes living in his belly-button lint. Zimmer’s “navelome” included 53 species of bacteria. One microbe had been known, until then, only from the Mariana Trench. [emphasis mine]


That explains why my 3yo and I can spend 2 hours together in the park talking to imaginary animals…


Is there a theory why there are no boys? Like, this syndrome is especially deadly to boys?


Getting half of my father’s genes was bad enough in my case.


I guess 25 out of every person tested in the world so far qualifies as “sometimes”…

It’s too bad that nothing good comes from it, but at least it’s not a common occurrence.


If I remember my biology right, XX is female, XY is male, and YY is unviable. Since this seems to be that one chromosome is (mostly) doubled, only XX would work. It’s been several decades since my last biology class, though, so I very well could be missing something.


That’s the “lies-to-children” version, but it’s correct enough in this case.


Given I was a child when I was told that, works for me. :slight_smile:


Most people don’t get DNA tested in ways that show this stuff up, even when they do get their DNA tested. I just read an article about a chimeric father who had his own cheek cells but some gonad cells from his absorbed brother. The first DNA tests he had said he wasn’t his child’s father. It took a further and less common test to say he was the uncle of his child, which led them to sample his sperm and figure out the story. Some of his sperm was his and some was from the ghost brother. We’ll start seeing more and more of these cases discovered as more people get their DNA tested more and more extensively.


This makes me wonder about the popular tests used for genealogy. Hopefully, they don’t all use cells from the same area. It would be great if more extensive testing didn’t mean more invasive procedures, too.


I used to be slightly jealous of some species females Parthenogenesis ability. This is even better!


Paternity is always a fraught issue, but it’s even more confusing in cases where the DNA test says that a woman isn’t the mother to her children because of chimerism.

It was all his, though - he is the “ghost brother” as well.

I was reading about some study that looked for Y-chromosomes in the brains of deceased elderly women. They found them in 60-something percent of cases (some of whom had never had children, and thus were likely to have picked it up from older siblings via their mothers). So DNA from pregnancies doesn’t just persist for “years” but potentially for life. Genetics is so, so much messier than what gets taught in grade schools.


There is so very little genetic information on the Y chromosome (compared to the X chromosome), that if an embryo only had the Y, or even 2 copies of the Y, there would not be enough instructions for the embryo to keep developing.




Sheeee-it! That’s a deep navel!

(Fascinating stuff. Thanks for sharing it)

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