This vacation I had a chance to watch some TV, in addition to spending time with the family, reading some books on wine and music, etc.
The most eye opening thing that I saw over vacation was some TV show on human chimerism, with at least two cases where people did *not* have any visible/physical signs of the genetic condition, but where they had two full sets of DNA in their bodies.
The term, "chimerism", comes from Greek mythology and refers to a multi-headed creature combining serpent, goat, and lion physiology (picture).
Now in human chimerism, there can be very visible markers. For example, in some reports of human chimerism (which is very rare as I understand things), people have documented checkerboard skin patterns on the chest where there is essentially a line going down the middle of the body, and where alternating squares (perhaps one inch by one inch blocks) of skin have light and dark pigmentation. To a casual observer, the checkerboard pattern may look perfectly square. In other reported cases, the person has adopted both male and female DNA. Again with a line going down the middle of the body from the head to the belly button, one half of the body may have male organs versus female. Surgery may be required to adjust the person to reconstruct the person as one sex or the other.
What blows my mind, however, is the case where the person looks and feels perfectly normal. As in turns out, it is believed that these people came to being by the fusing of two fully fertilized eggs as with Siamese twins, but because the cells did not split (say by day 4 of conception – don’t quote me on the specifics here since I’m doing off the top of my head), the embryo started to develop as one single baby with two *full* sets of DNA. Based on genetic, surgical, chemical, etc. research, it is believed that in these subset of cases that I am talking about, that while the person’s body consists of two full sets of DNA, any given organ may predominantly develop with one full set of DNA or the other (e.g., liver could have one full set of DNA from one egg, but the skin could have the full set of DNA from the other egg).
The cases caught on the TV show kind of blew my mind in terms of implications and how assumptions can be challenged. To make a long story short, two female chimeras from totally separate walks of life where shown to not have direct genetic connections to at least one of their children (by birth and eliminating possibilities of surrogate motherhood). One of the women was trying to prove that her kids were genetically hers, but DNA testing failed. Subsequent and more elaborate DNA testing showed that her kids adopted the DNA of some crazy combination of her father and her brother (this was after a court ordered that the birth of her forthcoming child be witnessed and have a forensic lab person collect blood, DNA material, etc. during childbirth – a DNA match between her and her child was negative).
DNA has often been used in courts of law to substantiate heinous crimes or to vindicate wrongly accused. DNA has often been thought of as having a one-to-one mapping with a person. Now the cardinality of the relationship may be challenged. (Note: to put some of this in perspective, however, the TV show stated that there may only be 40-60 cases [don’t quote me on number] of chimerism reported in the world, regardless of whether condition is physically visible)
Not a normal post by me by any means. But these are things that make me go …. hmmm. When I feel my (stereotypical) female traits coming through, well this discovery gives me moment to pause.
Update (2/21/06): See comments below on Siamese twins. It is likely that my reference to Siamese twins is incorrect.
I just wanted to thank you for all that important information about human chimerism.I’m doing a school health report about human chimerism, and thanks to you, I have alot of information for it now.
I saw the same show and am now wondering how many men have been determined not to be a childs father when they really are. And how many innicent people really are in prison wrongly?
I am doing some research, and your info was really helpful.
It is hard to put some of these numbers in perspective. But for aurgument’s sake suppose that the mechanism is via a crazy permutation of the Siamese twin phenomena. The probability of Siamese twins is 1 in 100,000 (per http://www.webmd.com/content/pages/22/108139.htm – did not verify or cross-check source). I would guess that the probability of human chimerism is much, much, much lower (i.e., close to a very, very miniscule subset of Siamese twin conceptions and then a fraction of that because you’d have to have a case where the markers were not visible … so would need to be male-male or female-female, etc.), especially given the sighting of only 40-60 cases worldwide.
I was intrigued to find your posting. For the past two or so years, I have believed that I am a chimera. I wish there was more information about it though. I have been two toned my whole life. Half of the back of my head has black hair and the rest is blonde. I have black chest hair ond darker pigment on half of my chest but the other is lighter and pale skin. The darker skin and dark hair seems to be only on the left side of my body. My mother was in her 30’s when she conceived me which would denote the possibilty of twins. If you have any more information on this subject, would you email me? Thanks
Scott,
I wish I had more information for you and others, but unfortunately I do not. I saw the show on cable (perhaps the Discovery Channel) in Las Vegas.
This posting really intrigues me…I just saw the same show last night on Discovery Health. I’d just like to discuss it a little bit and work out some of the logic in a case such as this.
First of all, I do not believe that it really has anything to do with Siamese twins or even Identical twins except being exactly opposite of that phenomena. As far as I understand about Siamese twins it only happens with IDENTICAL twins. Identical twins share the EXACT SAME DNA and come from only one original fertalized egg whereas FRATERNAL twins do not share identical DNA and come from two seperate fertalized eggs. Now, identical twins &/or Siamese twins occur because a single fertalized egg either completely or partially split apart and developed two bodies or in the Siamese twin case, two sets of body parts. Now, in the case of Chimerism it is the exact opposite. That instead of one single fertalized egg that has split apart into two identical twins, there is a set of fraternal twins with differing DNA that merges together into a single body. As in the case of the Texas baby that was half boy and half girl. The fraternal twins (one boy and one girl) merged together early in the pregnancy and developed into one body that was split down the middle with the left side male and the right side female. In the cases of both mothers on the tv show, I believe that both sets of DNA were female (so the fraternal twins would have both been female if they had not merged). Other than the Texas baby that had a normal appearing “whole” body except for the half male and half female sides, has anyone reading this ever heard of siamese twins (lets say joined at the head or hip or something – with two nearly complete seperate bodies) that were fraternal twins and not identical. Has there ever been Siamese conjoined twins with one being a male and one being a female?
Secondly, I’m wondering about what the differences would be between an all female chimera (like the women on the show) vs. an all male chimera vs. a male&female chimera like the child in Texas. The all female chimeras were obviously able to have children but would a male chimera be? Eggs are created in female fetus’ while still in the womb. Females are born with every egg that they will ever have but males continue to produce sperm throughout their lifetimes. Would this point make any difference? Would a chimeric male produce some sperm with one DNA and some sperm with the other? Scott, it certainly sounds like you would be a likely candidate as an all male Chimera (I don’t know much about your specifics though). Do you know if you are fertile like the women on the show were? Although it is not as striking as you are describing, I believe that my husband may have some of the signs of being an all male chimera. That’s why this particulary interests me. We have been married for five years and have not used any form of birth control in all of that time and have not yet concieved but as we have not yet decided to undergo any kind of fertility testing, we don’t even know if it is because of him, because of me or what. Anyway, would a child like the one in Texas be fertile and would it depend at all on the decision made by the doctors and/or parents as to which sex to make the child? The child in Texas was made “male” immediately following the birth. They removed the female reproductive organs and reconstructed the male organs but is “he” now fertile and if not, would this person be fertile if they had left the female ovary and its existing eggs intact instead? This is not even to mention the non-fertility related issues of a person that truely has half male and half female DNA, hormones, etc.
Finally, I also want to address my thoughts on the innocent being sent to prison based on faulty DNA evidence. I believe that it would be more likely that a guilty person was not sentanced that for an innocent to be charged with another’s crime. Let’s say that they found some hair at a crime scene and tested the hair DNA against a list of suspects. First of all, the suspects would need to be closely related to begin with. Second of all, it would depend on how they gathered the DNA of the suspects as well. One of the women on the show had some hairs from her head with one kind of DNA and some with the other. Her blood, however, consistently only tested as one of the DNA profiles. So, if there had been a single hair found at the scene of the crime that was not the same DNA profile as that of her blood, and the investigators tested her blood DNA, they would rule her out as a suspect because the DNA would not match. Now, two of her son’s would have the differing DNA that matched the hair sample but would also have their father’s contribution of DNA. Now, on the show they said that when they tested the larger family it appeared that the woman’s eldest two boys were the result of the woman’s brother and her husband so potentially they could make a very close match from the hair at the crime scene to the brother but it still would not be a perfect match. When looking at the childrens DNA they are only looking for a 50% mother match and a 50% father match where the hair DNA at the crime scene would presumably need to match its owner 100% which would not match the brother’s DNA by 100%. I believe that the closest that the investigators could come would be to say that it was definitely a member of the family but, without discovering that the woman herself was a chimera and profiling the matching DNA to the found hair, they could not conclusively prove that it was any other single person. So you see what I’m saying? If a chimera had killed someone but they could not single out a person with DNA that matched the evidence DNA 100%, there would be reasonable doubt and they couldn’t sentance an innocent person (like the brother, let’s say) based on DNA. It would more likely end up that the murderer would go free based on inconclusive evidence.
Anyway, I know that this ended up being a quite lengthy post but I’ve just been thinking about this and trying to figure out what it means. I’d really love to discuss it so please post back if you think I’m right, wrong or whatever. Many minds are better than one! 🙂
I also wonder how much that the ability for this to happen has to do with Stem cells in the womb and what this could mean to the medical industry. Perhaps in the future we will not need organ donors but will be able to “grow” replacement parts within our own bodies using donor DNA or even our own DNA!
Elicia,
“First of all, I do not believe that it really has anything to do with Siamese twins or even Identical twins except being exactly opposite of that phenomena…”
I think you may be right here in terms of the observation that it probably has to do with non-identical twins somehow getting fused during very early development. Somehow I recall the show saying Siamese twins, but perhaps my memory is incorrect. In any case, my intent was just to parrot back what I remembered.
As for the all-male chimera case, I cannot comment on this. It’s funny that this post should get so many comments and internet traffic. I only happened to see part of the show, and these notes were just from my post-vacation memory.
As for your comment about the innocent being sent to prison for faulty DNA testing, that’s an interesting point which I didn’t intentionally try to raise – I only tried to raise the point that most people think of the DNA to person mapping as one-to-one. Yet to address your point, I would think that there are some crimes where the suspects are closely related. Wasn’t there a recent case in the press where a brother was wrongly convicted and the brother came forward? All said, my initial impression would be as you state – it would probably be more likely for someone that is guilty to be found innocent in the case of some DNA mess-up related to chimerism. A more thorough look at forensic science, statistics and false positives/negatives, etc. would probably need to be done to sort this out!
Steve,
Thanks for your comments! I think this is just a very interesting conversation which is probably why you’re getting so many comments about it. I know you’re blog doesn’t usually involve this kind of discussion. It is interesting none-the-less and it did make me check out your other forums so … its not worthless, correct? 🙂
I did a little checking around and according to what I could discover on the internet … all Siamese twins are indeed identical twins and not fraternal twins. I find it intriguing that in the case of Siamese twins that the bodies can split and develope impartially into parts of two bodies but that in the case of chimerism that the two bodies seem to form one complete body with vastly different characteristics between parts. Just interesting that there has never been a sort of “Siamese” involving chimerism.
You are right about the question of one-to-one DNA to person matching. This just proves that as much as we ever think of something as a “scientific fact” that it could be found fallible tomorrow. 500 years from now, I am sure that our time will seem like the dark ages! 🙂
I am watching the above programme at the moment – I was so fascinated that my laptop came out and I happened upon your site… it’s entitled ‘The Twin inside Me’ and I have it recording from halfway through if anyone needs any more details, like the production company name etc. Looks like DNA based criminology is no longer infallible!
Hello, im doing a speech at school for my GCSE on chimerism. The information i gained from this sight is a great but i need some images for my power point presentation. Do you know where i could attain some from?
Thanxs Love Charmaine
Hai, i live in england, and i watched the same program u were talking about just last night and it intreged me.. i’d herad of the word ‘chimera’ from an anime i watch called ‘fullmetal alchemist’… and i didnt understand what it meant… but all the same the stuff involved in FMA freaked me out immensly… erm… yeah.. so… just thought i’d say my bit, came across this while trying to research chimerism!
Thanks for the comments everyone. Charmaine, I was not able to locate a picture of human chimerism on the net, but there is some interesting footage on the show if you can get a chance to see it. Good luck.
Siamese twins result from identical twins that do not fully separate. Conjoined twins comes from fraternal twins that do not separate.
I think chimerism is a reason for some homosexuality. Male body/female brain, and vise versa
Steve,
As the many others who have posted comments on your blog, I too just saw the discovery channel show on the chimeras women. I am actually wondering if you found any more information about it online or researches who have published their findings.
I am curious about this topic only because since day one, I have had red hair only on the right side of my head and from my waiste up only on my right side do I splotch when I tan. One of the splotches is along the mid-line of my stomach and is perfectly cut off when it would cross the mid-line. Fraternal twins happen to run in my family. I would like to learn more.
Have you found any other information that you think might help me, or even a researcher I could contact? I have had trouble finding anything.
Thank you!
Angela,
I have not found much more information on the subject, but I did find an older NPR recording here that may be of interest to folks.
http://www.npr.org/templates/story/story.php?storyId=1392149
Might also want to look at Google Scholar with the term “human chimerism”. On quick glance it was hard to digest this info, but perhaps there may be some leads for contacting people/researchers.
http://scholar.google.com/scholar?q=human+chimerism&hl=en&lr=&c2coff=1&safe=off&client=firefox-a&start=10&sa=N
I was also just watching the program on Chimeras for the 2nd time that spoke about a woman who was a chimera due to two separate fertilized eggs conjoining to develop one person with two sets of DNA. The program did say that had they (the eggs) conjoined any later in development it would have resulted in conjoined twins rather than one individual. This leads me to think that in theory siamese twins dont have to be identical, they could be the result of two conjoined eggs rather than one egg not spliting fully. Thus they could in theory, though extremely rarely, have two sets of DNA and even be male/female. I found a story that somewhat supports this about a child named May-joe who was born with one head and torso but with three legs and a hermaphrodite. However little is know about the child since it was in 1905.
And Kate, the terms Siamese twins and conjoined twins are pretty interchangable. Both are defined as a pair of identical twins born with their bodies joined at some point, a result of the incomplete division of the ovum from which the twins developed. A fraternal twin joining might be possible and similar to chimarism as I said above but is not in any published research that I know of and I have been looking pretty hard.
Hello. I saw this show (I am my own twin) last night on The Learning Channel. For the sake of hypothesizing, I considered the question, “What if genetic mosaicism is NOT, in fact, a rare condition, but instead an extremely common but very difficult to detect condition?” Suddenly the number of different human medical and psychological conditions that might have a chimeric factor to them expanded hugely. Multiple personality disorder, homo-hetero-bi-trans-sexuality, bipolar conditions, schizophrenia, heck just about any mental disorder really. Can anyone tell me how to find out if there is research into these questions being conducted yet? As an aside though, I am looking for some seriously information-dense science television. Any suggestions? It seems that lately every science show that I see on television is fifty minutes of filler, with a very tiny amount of science, usually pretty predictably placed at the 40 minute mark. Ten minutes of mushy science, then back for ten minutes of melodramatic ending. Is there anything out there that can be reliably expected to deliver at least 50% science?
There was a picture of a baby who was longitudeally split by color one of the child was brown the other caucasion. the narrator went on to say that genitally the child was also bisected. I have a loved one who is of dual gender who feels very isolated but is interested in varried forms of his condition when I told him of the boy he wanted to see for himself but I cant find a picture at discovery how do you access this?
There was a picture of a baby who was longitudeally split by color one of the child was brown the other caucasion. the narrator went on to say that genitally the child was also bisected. I have a loved one who is of dual gender who feels very isolated but is interested in varried forms of his condition when I told him of the boy he wanted to see for himself but I cant find a picture at discovery how do you access this?
Folks,
This is not a photo of what I saw on the original Discovery show, but it is a link to a picture on a related subject (but a very different skin pattern) …
http://www.thetech.org/genetics/ask.php?id=75
Kate: “Siamese twins result from identical twins that do not fully separate. Conjoined twins comes from fraternal twins that do not separate.”
This is not actually true. Though i can see how someone might come up with the idea.
Wow! I had no idea this was even a real thing. I was watching CSI the other day and this is what the show was about. A man that had committed a crime and the person he committed the crime against was positive it was him but the DNA evidance proved her wrong. In the end it was him. He had two sets of DNA. I thought maybe it was something that was made up for the show, but am amazed to find that it is real. It’s really very interesting.
it was very nice to go through this blog. usually we cant find that much informative blogs like this. thanks.
Very nice post. I liked your writing style and the way you covered the topic.
I thought that it would be pretty obvious, since the discovery of human chimerics has only recently be proven, that experts would not have thought to test siamese twins before to see if they are identical or franternal, since they assumed they were identical because they were conjoined.
It is not surprising that no known male/female conjoined twins have been discovered, as the chance of chimerism appears to be very small, and the chance of conjoined twins being born is very small. So you have to weigh up the probability of a woman releasing two eggs, them both being fertilised, by sperms of one X the other Y, the fertilised eggs then trying to merge and being unsuccessful, but the resulting embryo being viable enough to survive. Pretty small odds I say.
is it or would it ever be possable for a (male) chimera with the(working) inner reproductive organs of a female be able to potentially bare a child?