This refers to where a fetus in a multigestation pregnancy dies in utero and is partially or completely absorbed. This type of chimerism can be seen in what is known as the “vanishing twin” phenomenon. If this happens, the surviving fetus has two sets of DNA: its own DNA, and DNA from its twin. If a woman is pregnant with twins and one embryo dies in the womb, the surviving fetus may absorb some of the cells of the deceased twin. Remember, we all have unique DNA! Fusion chimerismĪnother type of chimerism can be more dramatic. You would then see that the genetic code is different. If you can find any, and sort them away from the mom's cells, you could compare the DNA from both sets. 3 But it isn’t always possible to do this, especially if the cells have similar characteristics. If they have different characteristics than the mother’s blood, it could be possible to tell them apart. Cells from the fetus can sometimes be found in the maternal blood stream. It may be possible to tell if a previously-pregnant woman is a microchimera. Just to give you some context, there might be 1 fetal cell for every 500,000 maternal cells. The level of exchange is quite small, so this type of chimerism is called microchimerism. If so, the woman essentially has a few cells that have her baby's DNA. Most of these cells die off, but occasionally a few may stick around. During pregnancy, some cells are exchanged between a woman and fetus. It turns out that most mothers are a tiny bit chimeric. If we ever needed to look at their DNA directly, we may need to look for other tissue types instead of blood. If you've ever had a blood transfusion or organ transplantation, you are probably a man-made chimera!įor example, a blood marrow recipient will have different DNA in their blood from the rest of their body. So the recipient will have two sets of DNA: their own (most of their body), and the donor's (in the donated organ). The goal is for the donor cells to permanently live in the recipient. When someone goes through either of these procedures, they are receiving cells (and DNA!) from another person. Anyone who has received an organ or bone marrow transplantation is actually a chimera. One type of chimera is actually quite common. Image from Wikimedia Man-made chimeras (organ transplantation) However, it is sometimes possible to find out if you are one! A mythical chimera. If this estimate is true, most chimeras must not know that they’re chimeric. However, the prevalence of natural human chimeras is hypothesized to be as high as 10%. A human chimera is made up of two different sets of DNA, from two different individuals.Įxperts aren’t quite sure how common natural chimeras are in the human population, as only 100 cases have been documented so far. In ancient Greek mythology, a chimera is a mix between a lion, goat, and serpent.
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