My mother, the Chimera

My mother, the Chimera

During grad school, I was amazed to hear that the color of hair on your body is controlled by only one gene.  Hence, each person should only have one color of hair everywhere on their body.  I wanted to ask:  why does my mother have two colors of hair on her body (or as the slang goes, the carpeting does not match the drapes)?  But I did not, at that time, have her permission to discuss this phenomenon.  Now I have her approval.   I have always wondered what the doctor doing her annual exams thought:  hmmm, she seems to be a natural redhead, I wonder why she keeps dyeing her hair on top brown.

zygote

Human zygote at the 4 cell stage.

Later I stumbled across a paper discussing the ideas of  chimeras in humans.1   Here I first read how an individual can come to be made up of more than one type of DNA.  The classical view is that each person is made up of one individual type of DNA which should be as unique as their fingerprint.  Hypothetically, if two fertilized eggs (zygotes) fuse together while in the womb and then merged together completely, you get what appears to be a normal individual, but made up of two different DNA types.2  I estimate human chimeras are born at approximately 1 in 50 live births, the same rate as for twins.

 What is a chimera, anyway?

chimera pottery

An ancient Greek plate, showing the original legendary chimera: a lion with a bonus goat head

What image does the word chimera bring up?  A lion with a goat coming out of its back?  The term chimera originated with the Greeks, describing a monster.   Using chimera to describe a human with two different types of DNA in the same body does not imply they are monsters.  Tetragametic chimerism sounds like you have cancer–human chimera just makes you sound cool.

 

chimeric mouse

Chimeric mouse on right, with two solid colored mice on left. Note in addition to different coat coloring, the chimeric mouse also has different colored eyes.

 

 

In the last century, the term chimera has been used to describe individual engineered mice born from a zygote derived from more than one type of mouse.  Chimeric mice have two fur colors on different parts of their bodies.  This is because the DNA that controls coat color is different in different parts of the mouse.  So when people, who had not been manipulated as zygotes, began to be detected with different DNA in different parts of their bodies, the term human chimera was coined.

So how can you tell if you are a human chimera? 

chimeric dog

Two different colored eyes are well known to occur in dogs.

Tell-tale signs are two colors of hair on different parts of your body, two colors of skin on different places of your body, or two eyes each of a distinct color.  The phenomenon of two different colored eyes is called hererochromia iridum.  The definitive method to determine your status as a human-human chimera is to have tissue taken from several different areas of your body and tested to see if the DNA is all the same.  The expense and risk (anyone feel like having a piece of your liver removed?) generally is prohibitive, but given the rapidly lowering price of genetics testing, it may soon be within financial reach.

Or you may be completely unable to tell that parts of your body arose from two different zygotes.  You may only get the news if there is DNA testing of you and your children; or if you are trying to get an organ donation from relatives, to whom you are no longer a parent according to the DNA.  Yes, this really has happened.

Any twins in your family?

Jane Seymour

Given her two different colored eyes and twins running in her family, it is likely (I’ll give you 95% odds) that Jane Seymour is a human-human chimera.

Another way to determine the probability that you are a chimera is the prevalence of twins in your family.  My grandmother was the sibling of one set of twins and aunt to another.  When I brought up my mom’s chimerism at a family gathering, my aunt, wanted to know if she was a chimera.  Sure enough, her eyes are different shades of green/hazel.  So I would conclude that she is also a human-human chimera.

Let’s look at Jane Seymour.  She has two different color eyes, a sign of being a human chimera.  Her most recent children are twins.  Twins run in families.  So, as in my mom’s situation, it is likely that her mother had two eggs available for fertilization at the same time. The twin information along with her two different colored eyes leads to the conclusion that Jane Seymour is most likely a human-human chimera.

In closing…

Mike Scherzer professional baseball pitcher

Mike Scherzer, a professional baseball pitcher for the Detroit Tigers, clearly has one light blue and one brown eye.

All the examples given so far are women who are chimeras–what about men?  Questions of paternity are nothing new.  But what if a man was pretty sure he was the father, but the DNA tests said no?  There are certainly ways of testing to show that the father of a child in question is related to the uncle degree.  But what if the father has no brothers?  I leave other scientist and lawyers to explore these questions.

So now my Mom can think of herself as her own twin.  Or she can make jokes about how this explains why she has the energy of two people.  Or if she wants to stump her doctor, she can say that she suffers from tetragametic chimerism,

______________________

1  “Embryogenesis of chimeras, twins and anterior midline asymmetries.”  CE Boklage.  Human Reproduction.  2006.

2  The following paper offers a different hypothesis to explain the formation of chimeras.  Read at your own risk. “Traces of embryogenesis are the same in monozygotic and dizygotic twins: not compatible with double ovulation.”  Human Reproduction.  2009.

DeeAnn Visk, Ph.D., is a freelance science writer, editor, and blogger. Her passions include cell culture, molecular biology, genetics, and microscopy. DeeAnn lives in the San Diego, California area with her husband, two kids, and two spoiled hens. You are welcome to contact her at deeann.v@cox.net

20 thoughts on “My mother, the Chimera

  1. Bill

    Thing about chimersim not mentioned – some people have both male DNA and female DNA. This makes mosaicism/chimerism a very likely cause for a number of sexual identity and gender identity issues.
    For example during the height of the AIDS epidemic in SF, autopsies of gay men noted hypothalamuses that uniquely resembled a female’s, and autopsies of gay male sheep have noted the same characteristics. It could well be the hypothalamuses controlling sexual attraction being of the opposite sex causes a same sex attraction.
    And in intersex persons with Androgen Insensitivity Syndrome, it could their 5% female dna body part that changes all the male hormones in the fetus into female hormones. So you get child with a female body, no males hormones at all (unlike most women), that identifies as a girl, looks more like a girl than may girls, can only have sex as a girl – but has descended testicles where a woman normally has ovaries. This is usually only discovered at puberty due to no menses.
    Recently intersex AIS women have been implanted with donated eggs fertilized by their husband’s sperm, and carried and given birth to children too.
    So chimerism is an explanation for many less usual sexual issues – but it isn’t a defect, or a mutation, but as normal as the occurrence of twins.
    Which suggests historical mistreatment of LGBT persons is even worse a wrong than previously thought, as it is due to very common biological reasons.

    Reply
  2. emogene

    What a great post! Thanks for writing this; just discovered it today. I was very interested to learn about the hair gene. I have always had a blond eyebrow and a brunette eyebrow, different color lashes on each eye, and a few patches of very blond hair on my head of light brown hair. I have suspected that I was a chimera, but when I used to ask doctors about my hair color, they said it was probably bleached from sitting on one side of a car(?) and that the hairs would all darken when I was an adult. I’m nearly 29, have hardly spent much time in cars for years, and the blond spots remain — it’s clear to me they’re here to stay. Is genetic testing still so expensive?

    Reply
    1. admin Post author

      Welcome to the chimera club!
      You can try various companies for sequencing. There are a few snags, however. The first is that you need to have the sequencing done twice, with one sample from each area (maybe from the skin right next to the hair of one color and another sample of the skin next to a different colored hair?). Most companies are set up to handle samples from saliva or blood, so this is harder than it sounds. If you can get a company to do this from skin samples, known more formerly as a skin biopsy, you next have to persuade a doctor, or other health professional, to cut out the sample.
      The second snag is that the federal government is concerned that we will all go running around like chickens with our heads cut off if we get our genetic data without the filter of a healthcare provider. Seriously though, people can get a little freaked out by relatively minor blips in their DNA. So to get the test done by say Illumina (http://www.illumina.com/clinical/illumina_clinical_laboratory/how-to-order.html) may require a doctor’s order. And I can pretty much guarantee that your health insurance will not cover it.
      Third, if you do get past the first two hurdles, is a more complicated problem: you are conducting research on yourself. But I recently read an article that a student wrote about where on the body was it most painful to get a bee sting. He needed no ethical review to use himself as a test subject, so using that example, you could do this experiment on yourself.
      Finally, you have to interpret the results. Again trickier than it sounds; not sure if I could do it if you just handed me the raw data.
      If you are independently wealthy though, I am sure this project could be done for less than $50,000. Heck, call Illumina at the number on their page. They may even be able to provide you with a genetics counselor; not so sure about getting help with the skin biopsy.
      My last thoughts are that you if you ever need an organ transplant, it might be nice to know it you have two different sets of DNA. This, I believe could be seen as medically necessary. Here is the company I recommend for that kind of testing: http://www.seattlecca.org/Chimerism-Testing.cfm They claim that their method of testing can “verify genetic identity of putative identical twins”. Elsewhere on the site the say they say they can work from a skin biopsy. Their test is not a full genome sequencing, but if it can distinguish fraternal from identical twins, then it will answer out question. It does look like they are set up to handle skin biopsies.
      You are welcome to call them and see how much it would be to get the twin testing done on skin samples. But you may not get far, unless you have a medical degree yourself, or a doc to order the test for you.
      Let me know if you ever get this done–I’d love to know the results.
      Best,
      DeeAnn

      Reply
  3. Gloria Henderson

    Very interesting and very well written. I’ve seen plenty of odd-eyed dogs and cats, but not so much with people. Thanks for enlightening me on this phenomenon.

    Reply
  4. Jessica Behymer

    My hair is split almost exactly down the center part with very pale blonde on one side and brunette on the other. My eyelashes are dark on the brunette side and very light blond on the other. Family history of twins on both sides, though not for the last few generations. I always thought it would be interesting to have formal testing/research done.

    Reply
    1. admin Post author

      Jessica, congratulations, you are now a member of the human chimera club. Maybe we should start a Facebook page, huh? No one that I know of is doing research on this. You could always try and get two whole genome sequencing done on your body (just make sure they use tissue from both distinct sides. It should only run about $3000. I would love to be able to do it for my mom, but other are other things to spend your money on! What we need to do is find someone to fund the research.

      Reply
      1. Jessica

        Having our own club would definitely be interesting! There truly are so many other things to do with $3000…but if it were someone else sponsoring the research, it would make the decision MUCH simpler. Where shall we look for such a person?!?

        Reply
  5. Romina

    There was an episode on discovery channel called I am my own twin were this lady was acused of fraud when she applied for wellfare assistance in london and the maternity test was not a match, oddly enough the children were a match to the dad. She was pregnant when they tested her newborn the same results happen…. Super interesting. It’s a nightmare for the court sysytem cause somebody can comit a crime and yet the dna they leave behind is not the same as the one that could be tested…. I enjoyed your article! Bye mitochondrial dna helped in one of the cases.

    Reply
    1. admin Post author

      Romina,

      So glad you enjoyed this article! I had a lot of fun writing it. It is always the exception to the role that makes things tricky. DNA evidence is compelling, but not always infallible. Glad to hear they were able to use mitochondrial DNA in this case.

      DeeAnn

      Reply
  6. Jess

    The picture of the collie with two different coloured eyes and patchy body? It’s called Merle. It’s a dominant colouration gene which, along with the body colouring, can give two different coloured eyes and also can produce eyes with both blue and brown in the same eye. I have a merle Australian Shepherd, her father was also merle and has the two colours in both eyes. Differently coloured eyes are very common in merles, it’s part of the package of the colouration.

    Reply
    1. admin Post author

      Jessie,

      I need to research this and get back to you on it. I think that you may have given me a lead for another blog. The new blog would be about animals (including humans) that have white hair and blue eyes.

      Stay tuned.

      DeeAnn

      Reply
    1. admin Post author

      Lisa,

      The two sisters mentioned here could potentially have organs that has a completely different (as sisters can be) DNA make up. So maybe their livers (made with one type of DNA) could better fight off an illness than if it were made of the DNA found in another part of their body.

      Children of these sisters would not really be any more diverse, unless they too showed signs of chimerism.

      DeeAnn

      Reply
  7. W. Garzon

    I found this very interesting. I liked your writing style. My son instantly pulled out his book of Percy Jackson, The Lightning Thief, to point out where he had read about chimeras. Keep up the good work.

    Reply
  8. D. Williams

    Interesting article. I like your writing style. Hopefully this will begin more discussion on the matter.

    Reply

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