Genetic chimera

[arcticpenguin]

I heard a story on NPR this morning about genetic chimeras.

The usual, textbook, arrangement is for humans to have the same chromosomes in every cell in their body.

However, in rare cases they are discovering that some people have two different sets of chromosomes in different cells. The proposed origin of this is that two embryos merged into one, i.e. two fertilised eggs that should have been fraternal twins combined into one embryo, resulting in different parts of the body having different copies of genes.

This has interesting implications for DNA testing in criminology, testing of ancestry and organ transplants.

 

[Javalar]

This has interesting implications for DNA testing in criminology, testing of ancestry and organ transplants.

Wouldn't it be weird to be like this and have, in fact, two different fathers? Although it's very improbable, it's not impossible.

 

[Jon_in_london]

Check out the geep!!

http://arbl.cvmbs.colostate.edu/hbooks/genetics/medgen/chromo/mosaics.html

{pic too big to post]

 

[Hexxenhammer]

I heard this story too. Very cool and bizarre. What brings it home is the fact that the woman in the story is her kids mother AND AUNT at the same time.

 

[Dymanic]

Originally posted by arcticpenguin

This has interesting implications for DNA testing in criminology, testing of ancestry and organ transplants.

The famous biologist, Stephen King, explored some of the possibilities in his book, The Dead Zone. I can see it now: "It wasn't me, your honor, it was the evil twin that lives inside my brain."

Originally posted by Javalar

Wouldn't it be weird to be like this and have, in fact, two different fathers? Although it's very improbable, it's not impossible.

Yes, I've seen photographs of people who appeared to be attempting to accomplish this.

 

[Doubt]

I also heard that one this morning. I wonder about how the two different sets of genetic material work together for one person.

Do these people have some organs with one set of genes and others with the different set? Are some organs a mix of the two? Why does them immune system not attack parts of the body that are genetically different? Why don’t these people have obvious mutations such as extra body parts?

 

[Phaycops]

The famous biologist, Stephen King, explored some of the possibilities in his book, The Dead Zone. I can see it now: "It wasn't me, your honor, it was the evil twin that lives inside my brain."

I thought it was The Dark Half.

 

[Hexxenhammer]

Do these people have some organs with one set of genes and others with the different set? Are some organs a mix of the two? Why does them immune system not attack parts of the body that are genetically different? Why don’t these people have obvious mutations such as extra body parts?

Don't know the answer to the last two questions, but the answer to the first is yes. The woman in the story's blood and some organs had one set, and her skin and some other organs had the other. Some organs were a mix of the two.
Here's my non-biologist thought. The twins integrated very early, just a few cells apiece, forming a cohesive whole. When organ differentiation time came up, some cells from one twin became say the stomach and digestive system, while the blood and bones arose from stem cells with the other genes. This creates a patchwork genetic makeup with some systems with 1 set of genes and other systems with the other.
Any biologists want to critique? And the question of why the body doesn't attack itself is a good one. Anyone know why?

 

[arcticpenguin]

I think immunological auto-recognition (fancy words for why the body's immune system doesn't attack itself) happens in the thymus, so that's not inborn, it's a process that happens. I can't remember whether this is at a particular time in development or if it's an on-going thing.

 

[Jon_in_london]

Why does them immune system not attack parts of the body that are genetically different? Why don’t these people have obvious mutations such as extra body parts?

Because the immune system will 'grow up' recognising both as self.