This is a good video explaining chimerism. It deals with cats and human beings, but the general concept is the same for horses. (Thank you, Joanie, for sharing it!)

I sometimes get asked why I do not often discuss brindles. A large part of it is that, as a fraternal twin myself, I find the type of chimerism responsible for brindle in horses – called tetragametic chimerism – disturbing. There are other forms that do not involve the fusing of two embryos into one organism, as the video explains. The video talks about microchimerism, where genetic material passes from the fetus to the mother. There is also blood chimerism, where genetic material passes between twins through a shared portion of the placenta. A certain portion of fraternal twins are blood chimeras. Because I have had a conflicting blood type test in the past, and because my twin had a different blood type, it is possible that I am part of that group. (It is also possible that I had perfectly ordinary blood and a careless individual performing a blood test.)

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11 Responses to Chimerism

  1. Dainelle Kinsel September 29, 2012 at 9:55 am #

    Hey Lesli! Could you please elaborate on what you find disturbing about chimerism? Your posts are always so thoughtful and scientifc, and this comment seems incongruous with your former thoughts. I am just curious, not trying to critisize. I’ve been fascinated with the idea of chimerism in organsims for many years and am always looking for more information! Thank you, DK.

    • The Equine Tapestry September 29, 2012 at 10:21 am #

      Tetragametic chimeras are two separate organisms (twins) that have merged together in utero to form one organism. Many people find this concept a bit creepy. Since I grew up with a living twin, the idea of one of us being partially absorbed by the other (and no longer existing, or sort of existing?) is particularly distasteful to me. Not an entirely rational reaction, but then none of us are rational 100% of the time. 🙂

      • dakota328 September 29, 2012 at 1:10 pm #

        I was to be a twin. Due to a placenta defect the other one didn’t make it. Though it was later in the pregnancy so no chance in myself being a chimera. Growing up without a twin when you were supposed to be a twin really isn’t that big of a deal. Thinking I would have absorbed the other one does seem odd, but really, instead of me my mothers body did to get rid of it so I could continue to survive. For myself, and knowing others on here how love to learn things, I don’t see chimera being an off putting topic.I find chimera things fascinating and would love for you to someday do posts on them.

  2. Nikki Byler September 29, 2012 at 10:27 am #

    You got the wrong video. you should not have seen that video first. Chimerism is not something that is disturbing, it’s rare, but natural. Things like this happen because we don’t know about how things work, or don’t in this case. It should not be disturbing.

  3. peg4x4 September 29, 2012 at 10:37 am #

    The world is an amazing place.
    But I don’t belive the cat is a chimeria. Seen too many tortis with that sort of markings.
    The chimera discovery may have use in organ transplants..

    • The Equine Tapestry September 29, 2012 at 11:09 am #

      I agree about the cat, which of course is also the position of the person in the video.

      • peg4x4 September 29, 2012 at 12:47 pm #

        This one case will be a boon for the lawyers.
        I wonder how many stallions/mares have produced offspring that just wern’t “right” for the genotype..
        The more we learn,the less we know 🙂

        • The Equine Tapestry October 2, 2012 at 8:25 am #

          I suspect that the widespread use of parent testing in registries will make it more likely that chimeras will be identified when they occur.

  4. TBA October 1, 2012 at 10:51 pm #

    I just saw this really interesting horse on pinterest, I don’t know if this is something you’ve covered already, but I thought it was fascinating: Hopefully you can see it through that link!

  5. malibupets October 27, 2012 at 11:03 pm #

    Here’s an interesting labrador, perhaps a chimera or mosaic. The pattern reminds me of an African Wild Dog.