Chimera Twins Story

skelley writes "Below is an audio link on this morning's story on NPR about Chimera twins, or people with two sets of DNA. It turns out that every once in a while a set of fraternal twin eggs merge into one embryo. The resulting person has two sets of DNA. The story says it is possible for a Chimera to have different sets of DNA in different body parts. This can cause complication for body identification, DNA typing for organ transplants, crime investigation, etc. Researchers have no idea how common this is, but suppose that it is a reasonable percentage of all fraternal twin pregnancies, which would mean millions worldwide. No text version. NPR often doesn't publish one. "

Comments

Another great article

[Blangopolis]

Anther great aricle about Chimera twins that I was reading eariler is here. Man this stuff is really interesting. It actually says that about 8% of non-identical twins are chimera twins. That's actually pretty high.

Since you can't RT{F}A

[zubernerd]

Since NPR only provides an audio link, here are some text sites with info on chimeric twins (genetic mosaics).
[Genetic Mosaics] http://users.rcn.com/jkimball.ma.ultranet/BiologyP ages/M/Mosaics.html
Google search for Genetic Mosaics
And for the non-biologists

Re:Odd

[Hentai]

Well, IANAMB (I am not a molecular biologist), but I would assume that if the blood or tissue types were incompatable, the embryo would very quickly become non-viable, and the body would take care of it in the normal way (remember - only about 15% of all inception results in birth; the rest are spontaneously aborted.)

I would imagine that the number of viable chimeric embryos is much lower than the total number of chimeric embryos; in fact, you could probably graph something like an inverse logistic curve of surviving chimeric embryos vs. days of pregnancy.

Re:It's not uncommon

[timbloid]

Was it this one?

Re:finally, a valid excuse

[socrates32]

Try this explanation.

And another genetic anomaly heard from

[Tsu Dho Nimh]

It doesn't take "chimerism" to get this effect. The well-known variations in the number of sex chromosomes can also do it, and they can happen in the cell division process.
Normal male = Xy (any extra "X" are abnormal, but even a XXXXy is still male - all but one X gets deactivated - but usually has serious medical problems). Normal female = XX (extra "X"s do not create supermodels, it creates medical problems)

Take a look at any calico or tortoise shell cat. What you are seeing is the result of random deactivation of one of the X chromosome early in the development of the embryo, and the random appearance of the colors (black or orange) on that chromosome. Humans have few easily testable traits that are testible for chimerism: one blood group is all I can think of at the moment, that "lives" on the X chromosome.

For calico or tortie males (yes, they exist, and no they are not valuable) the division between the colors is a good indicator of how badly screwed up their sex chromosomes are. A male that is mostly orange with one small black patch probably acts like a tomcat and will show very few cells of the XXY pattern, and might even have that abnormality limited to that spot. One that is well-mottled with black and orange is probably not interested in breeding and will show mnay more abnormal XXY cells.

In order to test this for the possibility to screw up DNA identification, they could start by testing the known chimeras - cats.