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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.
"
so now when your liver commits a crime, it can be convicted seperately?
I would like to be able to decide which of the two sets of DNA are set as 'active' at a given time. That would be nice for things like murdering my wife and whoever she is sleeping with outside of our house, and then getting away with the crime.
If the DNA don't fit.. well.. uhh.. ahh shit.
"My evil twin brother did it. Honest."
The interesting thing is that since invitro fertilization has a much higher probability of twins (or more), chimeras will become more common.
This is perfect for /. It's impossible to RTFA
Laugh while you can, monkey-boy!
No text version. NPR often doesn't publish one.
Oh ho ho, methinks they'll change their mind very shortly.
One of the X chromosomes is mostly disabled a little bit past conception (after the cells have divided a good amount though). However, which one is disabled is random at this time, which means different regions of the body derived from the original cell will have different X chromosomes disabled (into what's called a Barr body). This is all very screwy which is why females are very screwy.
-Libertarian secular transhumanist
Any known birth defects/oddities arrise from this which manifest themselves in the physical sence? IE if your trying to test someone's DNA and realise they have blond hair on one half of there skull and black on the other you would know something was up.
O.J. is INNOCENT! It was my.... uhh.... other DNA...
Check out our infosecurity industry blog: http://securitymusings.com/
...but do they have +2 attack strength?
Ah, computer dating -- it's like pimping, but you rarely have to use the phrase "upside your head" -- Bender
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.
Wouldn't this cause complications a little more important to the individual than those listed? Like say, stuff not fitting together right? I mean, I wouldn't want to try and build a working car from half Ford Explorer parts and half Ford Focus parts.
I wonder how many people with this condition die before birth or at a very young age.
Nature published a short article on this a couple of years ago that we covered in our Journal Club meeting at my lab. The only one people detect right now are chimeric male/female twin pairs because its so easy but they had lots of cool shots under UV light where you can actally see like tiger striping of the two chimeric skin types. That was my favorite part.
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 NPR only provides an audio link, here are some text sites with info on chimeric twins (genetic mosaics).P ages/M/Mosaics.html
[Genetic Mosaics] http://users.rcn.com/jkimball.ma.ultranet/Biology
Google search for Genetic Mosaics
And for the non-biologists
Accentuate the positive, don't waste your mod points on the negative.
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.
-Hentai [in vita non pacem est]
In Greek mythology the Chimera was part lion, goat and serpent. This is why people with organ or limb transplants are sometimes referred to as a Chimera. So my question... do these people also present the same identification complications?
It's just his white Chimera brother finally coming out after all these years.
The human genome isn't like the automarket...That is you're still building 1 car, but all the parts can be slightly different, but come from 1 supplier. After all, in a normal diploid animal (ie. humans) half of the chromosome content is from the mother, the other half from the father. As far as liver, heart, skin, etc. all working together, there is no problem with this.
There is a problem though with the immune system. Since each organism's cells contain a unique combination of cell surface receptors that let's their body know the difference between "self" and a bug or virus, then depending which copy of DNA founded the cells of the thymus (where "self" is first determined), a chimera's immune system could see cells with the other DNA set as foreign - causing a massive systemic allergic reaction. The good news is that chimeras with this problem would spontaneously abort within the first few months of the pregnancy, so if a chimeric human is born, they probably don't have to worry to much about such genetic mismatches.
"Nokia is not a country, it's the capital of Finland!" -Moderated "Informative". Yeesh.
Now that I've got that out of the way... I'd say that quite often since differentiation of cell occures very early on, and that often the other allele in the pair is inactivated, it may be that one tissue type is derived from the one set of genes, and another type is derived from the other set of genes. That person may be a a higher risk of developing auto-immune diseases. Your proposition of spontanious abortion is quite possible... but remember Jurassic Park (life will find a way!).
'Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?'
Actually, I know of one case where this was so. I used to work with a guy who was a chimeric twin. He volunteered for some genetic research at Stanford and they came back and said he had two sets of DNA. He had one of the oddest shaped bodies I've ever seen. Looked kind of like something from Star Wars - like a ball perched on top of really long legs.
Am I the only one who read the title and thought, "Finally! All this messing with genes has produced something useful, a fire-breathing Chimera with a lion's head and a goat's body"? On a more serious note, the nature article in a similiar vein is here.
I Am My Own Worst Enemy
IANAMBBMWI (I am not a molecular biologist, but my wife is).
This isn't as big a problem as you'ld think; as long as the two embryos merge before the cells start to differentate it could work.
There are some really creepy experiments with mice where they did this on purpose with white and black mice, and got striped (!) mice that always had exactly 13 stripes (well, sometimes adjacent stripes were the same color, but if you made enough mice you could tell) - this told them that the skin developed from 13 cells, etc.
Presumably if you're mixing siblings you won't get stripes...
While I don't know for sure if I am a chimera, I was born with XX/XY sex chromosomes, something I only found out in my early 20s.
For many of us born this way we don't appear to be completely male or female and like most I was surgically "repaired" very soon after birth. This means I had what appeared to be testicles removed, testicles which MAY have permitted me to have children one day. Part of my body was stolen because I looked different. I was raised female, always felt that didn't quite fit, and it took me a lot of messing through courts to obtain my birth records. As I am now I have to settle with knowing where I fit originally, why I am like I am, and can accept living as a mostly normal female. By nature however, I was born part male part female. That's me. The chance to live and develop naturally was stolen from me.
It's fucked. Science continues to find so many variations on human development but society so often manages to force decisions on people. How odd that I was considered unnatural enough when I was born that doctors decided surgery was the only acceptable option, when my birth and very existence is just one more facet of nature.
For more info on how intersexed kids (chimeric or any other variation) are treated, see isna.org
Not a problem in this case; the immune system hasn't 'initialized' at that point, and so would imprint both types as self when it comes online.
This is why people are interested in freezing fetal blood samples; the theory is that you keep a backup of the immune system install media to reinstall if it goes bad. Um, except that we have no idea how to do that yet... works in theory, though.
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.
IANAL, but IUTWIBB ... I used to work in blood banks doing crossmatches. A small number of people have two different ABO blood types. They are not "AB", they have some red blood cells that are pure "A" and some that are pure "B" and that is violating Mendelian genetics. The same mechanism that creates this could easily create other "blood chimeras" with the other several hundred lesser-known blood types. And a third mechanism (sex chromosome abnormalities) can create a kind of blood chimera that has nothing to do with twins.
Apparently, most of these blood chimera individuals shared a blood supply with a non-identical twin before birth (the cells that make blood and populate your bone marrow float around the fetal blood supply while waiting for bones to develop to give them a place to settle, and the placentas and their blood vessels can merge without producing conjoined twins). In some cases, people are unaware that they had a twin because he or she died early in gestation and was spontaneously aborted (or disintegrated by the mother's defense mechanisms, or walled off in the mother or living twin). They show up in the National Enquirer when someone is operated on for a cyst and it has bits of the encysted twin in it.
As many as 8% of non-identical twins may have chimeric blood. Some people are microchimeric--they have a small amount of blood of a different type in their system that has persisted from a blood transfusion or passed across the placental barrier from their mother before birth.
"Blood chimerism" does NOT cause a problem for the person with the chimerism as far as receiving blood in a transfusion ... they will tolerate any phenotype they possess if you transfuse it - they have had it since they were fetuses and it is "self" in the immunological sense of the word.
It can, however, be hell on blood banks trying to figure out what the heck is wrong with the blood during the initial typing and screening in a transfusion where the blood chimera is the donor. The potential recipient is not at risk because the tech says &^$^$#%@!!!, sets the donor unit back in the frig with a "do not use" note and sends it off to a research lab to find out what's going on. That's how you usually find blood chimeras and new blood types ... anomalous results in what should be a routine crossmatch.
Cool! I found a picture of those striped mice. Some more pictures:
Closeup before eyes are formed.
In-vitro development in the lab.
Displaying remarkable inteligence as they swarm and are about to devour their much-bigger and unsuspecting prey (apparently striped mice are carnivorous)
HIV Crosses Species Barrier... into Muppets
Probably it was just a joke. The statement: "Thank god I'm an atheist" implies that the person believes in god.
Then again, maybe its because he is an atheist and wants people to be aware that there are differing viewpoints. A great many Christians in the US seem to think that everyone else in the country is also a Christian. Stating that you're an atheist is similar to driving around with a Jesus fish on your car.
And, just as an FYI, warning an atheist about hell has about as much effect as telling the average adult that if they misbehave, Santa won't bring them any presents. In other words, none.
psmylie's dictionary: Godzillion (noun) Any number large enough to destroy Tokyo
It's kind of odd this got modded interesting when the pictures are of chocolate mice. I suspect the moderators didn't bother to follow the links.
More often than not, things don't go right.
Everyone has heard of Downs syndrome, when a child has an "extra" chromosome. Well, think of having twenty three extra pairs.
I am a fraternal twin, and I don't know if I am a chimera or not, but my wife and I have had trouble with a similar situation of too much DNA. Last year, we had a molar pregnancy.
"What is that?" you may ask. A molar pregnancy happens when an egg is fertilized, but no baby is formed. It happens when the egg "looses" the genetic information from the mother (complete molar), or has three sets of chromosomes (69 total, partial molar). Molar pregnancies are about 1 in 1500 births, with 98% of those being the complete type.
Either way, it is a horrific experience, and should be considered cancerous. The mother's hormone levels will climb to dangerous levels as the mass of cells that should have been an embryo rapidly grow and divide inside the womb. She will become extremely pregnant, without a child, and morning sickness becomes a 24 hour a day nightmare. Relief only comes with complete removal of all molar tissue. After this, the mother has to be monitored and be "pregnancy free" for a year, to tell if any of the molar tissue has become cancerous.
Our case was a partial molar. If things would have gone right, we would now have a set of identical twins, but it didn't. DNA is a funny and powerful thing and too much is never good.
-- Len