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You know what's fascinating and also
a little bit gross when you think about it?
Chimeras.
Not the mythological ones
but actual chimeras:
organisms that contain the genetic information of more than one individual.
And yes, this is a real thing.
Chimeras are usually formed in the very early stages of embryonic development
when two zygotes fuse into one
and the resulting chimera basically ends up being its own fraternal twin.
Which is. . . yeah. I know.
And you end up with all sorts of weird conditions
like if you're a male and a female fraternal twin fuses into one
sometimes you get one ovary and one testicle
literally with different genetic information in them.
There's also this woman who needed a kidney
and so they did a blood test on her kids to see if they'd be good donors,
and they did it, and they were like "not only would they be bad donors
but they aren't your kids".
And she was like "Yeah, but, uh, they came out of me".
It turned out that her blood, and her organ systems, were from two different people.
They had two different genetic makeups!
So she gave birth to a different person than her blood would have . . . given birth to.
And I'll wager you a box of jujubes
that you've heard of the adorable two-faced cat with mismatched eyes, Venus.
She is often described as a chimera, but it turns out
that she's probably not.
Instead, she appears to be what most female mammals are:
a mosaic.
See, a female has two X chomosomes
one from her father and one from her mother.
But as an embryo, each of her cells deactivates one of those two Xs at random
so she ends up with two different groups of cells in her body:
One with only her dad's X
and one with her mom's.
In humans this differentiation is difficult to detect
because not a lot of traits are linked to those X chromosomes,
but in cats, that distinctive tortoiseshell coloration that Venus has IS X-linked.
So what we're seeing is probably the arrangement of her different 'mom X cells' and 'dad X cells',
that happen to line up down the middle of her very kissable face.
So Venus may not really be a chimera,
but try not to be too heartbroken, because you know who is?
I'm sure you know one, actually, because
you came out of one.
Just today, scientists in Seattle say that they've found the first evidence of male DNA
in the brains of women.
After performing autopsies on the brains of 59 women,
they found that two thirds of them contained different DNA
and it was male: XY, not female: XX
Now, the researchers don't know the history of each woman whose brain was studied,
but they suspect that the DNA got into their brains through whats known as 'fetal chimerism':
when a pregnant woman receives cells from her embryo,
which then go on to start lineages in the mother's body
that can last for the rest of her life.
This phenomenon, also know as 'microchimerism', was first discovered in the 1990s in women's blood,
but this is the first time it's been observed in their brains.
This could change current thinking about how widespread chimerism is in women
and also what implications it might have for the study of brain disorders
like Alzheimer's disease.
So, as if those nine months weren't enough, Mom,
you're still carrying a little bit of me with you wherever you go.
Thanks for watching this episode of SciShow Breaking.
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