CSI already beat you to it.
FTI, that exact case was documented in an episode of (I think) Forensic Files and is also talked about in the special I mentioned above, “I Am my Own Twin”. They give tons of details on the science behind it.
And you beat me to that post!
It was a pretty good episode, too. I remember watching it. IIRC, Grissom accidentally solved the case when he saw the guys back (he had taken his shirt off) and he noticed splotchy skin coloration, which is often a sign that the person is a chimera.
Bastards.
Even if a person is a chimera, the two sets of DNA will be as similar as any pair of siblings. Or conceivably half-siblings, if the two zygotes had different fathers, but I think that’s pretty rare to begin with, in humans.
Thanks for the answers I’ve read a lot, from what I read the woman who was her own twin, the DNA they took showed she wasn’t the mother but she had enough DNA to be related to the child as a grandmother. Of course when they took DNA from elsewhere on her body they found she was the mother.
Which brings me to the question, HOW is the DNA distributed?
Let’s say you witnessed the woman giving birth but the DNA didn’t match, so you think she’s a chimera, how many parts of the body would you have to sample before you found an organ with the DNA showing she’s the mother?
Are the two types of DNA evenly distributed or does it vary from case to case, and could it be more than two eggs that fused?
thanks for the answers so far
It varies between individuals. Some people seem to be an even 50:50 split. Some people seem to have only very small areas of tissue of a different type.
It varies, but it is never “evenly” distributed" insofar as the pattern will be approximately random. So for example someone might have all their skin as one genetic type, or it might be distributed in stripes across their body or it might be that the skin on the legs is one type and the skin on the upper body is another type.
In theory yes, but it is very unlikely to occur naturally in humans. The hormone system in humans makes it unlikely that more than two eggs could be released at the same time. The odds of triplets from different eggs occuring naturally is already remote, the odds of such an event resulting in a thee way chimaera would be about as likely as being kicked to death by a duck. Of course with the use of of various fertility drugs that promote the simultaneous release of multiple eggs the probability increases a lot. Most animals release multiple eggs simultaneously so I wouldn’t be surpised if it occurs with some regularity in animals.
[My apologies if this was answered in a link that I was too lazy to read.]
Are chimera always, or usually, or ~half the time formed from 2 embryos of the same sex?
And if the answer is not “always”, how does this factor in on transsexuals? I’m wondering what would happen if male and female embryos merged to form a chimera.
As far as I am aware, chimeras can be formed from MM, MF, FM, or FF combinations with respect to sex (M=male, F=female) with each possibility being equally likely. You’ve got a 50/50 shot of them both being the same sex.
In the wikipedia link above, it says the following:
I didn’t understand this bit in the article. Pretending that I am a chimera (or perhaps I am, I guess I wouldn’t know if I didn’t have a reason to), if I have a MF or FM combination, is it automatic that both genitals would appear? The article seems to be saying that in some cases the amount of genetic material is very small – so why wouldn’t it be possible to have most of one’s body appearing with the DNA from one blastocyst, and say, an eye or something, of the other? Would having an M eye be enough to prompt the development of male genitalia if the entire rest of the body came from the F DNA?
Becuase of the way that the body develops. Essentially a single cell or a handfull of physically close cells adopt a certain role and continue along that line for the rest of development. At this stage when fusion is possible there is no eye, the cells will only be differentiating into ectoderm or at best “epidermis”, some of which will go to develop into skin, some into eye, some teeth and so forth. So it would be incredibly improbable to get a single isolated patch of tissue develop from a speciifc cell line. The entire skin of the head might develop from that cell line, but not 10cm^2 of tissue isolated in the left hand side of the head.
No, to get that sort of effect you would need to have the hormone secreting organs of the brain/ brain stem male. Those are the organs that control what hormones are released and those hormones in turn dictate how the genitals develop. Having a male eye is going to have zero effect because those body parts just don’t secrete the hormones that dictate the way the primary sex characteristics develop.
Can someone tell me, in layman’s terms, the difference between chimerism and mosaicism? I get that in chimerism there are two distinct zygotes and in mosaicism there is one but after that the Wiki article loses me.
In mosaicism, are there mental or physical disabilities associated with it?
Well, there isn’t much more than the two vs one zygote thing. And since the mutation can sometimes be chromosomal (ie, an extra Y or X chromosome), that can lead to some pretty dramatic changes. The general name for this condition is “trisomy”, meaning 3 chromosomes (instead of 2). One of the more commonly known trisomic conditions is Downs Syndrome, which is an extra copy of chromosome #21 (sometimes the whole chromosome, sometimes just part). As the article says, people with mosaic trisomy general exhibit the same symptoms as trisomy in general, but in a milder form.
More accurately, she would be closely enough related to be the child’s aunt, since effectively, that’s what that genome was. But an aunt and a grandmother are both equally related to the child (on average, at least), so the statement that she was close enough to be the child’s grandmother is still correct.
On the subject of gender-mixing, I would naively expect that many chimeric embryos would be nonviable, and that the viability would depend on how similar the two genomes were. Would this have any impact on the rate of intersex chimeras, via an intersex chimera being less likely to survive to birth?