Are You Your Own Twin?

Johnny 2 Lydia Fairchild was surprised to be informed that she was not the mother of her children. “I knew that I carried them, and I knew that I delivered them. There was no doubt in my mind,” Fairchild said. She and her family were taken to court after some routine DNA testing to prove that they were all related after she applied for welfare support. The tests indicated that Fairchild’s boyfriend was the father of her children, but that she was not, apparently, their mother. Lydia Fairchild was taken to court for fraud. How could a mother not give her offspring her half of their genome? The answer lies with the woman’s developmental history in a phenomenon called chimerism, specifically tetragametic chimerism. Chimerism occurs when two separate sperm fertilize two separate eggs, but then the two separate embryos fuse together at the blastocyst or zygote stage. Because the tissues from the two different embryos may not integrate completely, the developed organism may end up with their absorbed twin’s kidney, or one of their pupils, or, as in Fairchild’s case, gametes. Once chimerism was believed to be rare, but evidence is starting to point that it is more common than scientists believed. Most people have some cells that are genetically identical to their mother’s and most mothers have cells that are left over after they give birth to their children. This is called microchimerism. For other species, chimerism is the norm. The male anglerfish joins its body to the female during reproduction to form one hermaphroditic chimera. Marmoset monkeys give birth to offspring with their absorbed sibling’s genes about one third of the time. Fairchild’s chimerism was eventually realized, but only after every other option had been exhausted. Her obstetrician testified. The family ordered tests from different labs, thinking that there must have been a mix-up at the first one. The judge for Fairchild’s case came to the hospital to watch her give birth to her third child. Despite this evidence, DNA tests still showed that Fairchild was not the mother of her children. Finally, the lawyer for the prosecution found a similar story and realized Fairchild’s condition. DNA from a cervical smear test showed that the genetics of Fairchild’s reproductive organs matched that of her children’s. You may never know if you, like Lydia Fairchild, are a chimera. Or your ghost-twin may show herself in one hitchhiker’s thumb, or a blonde eyebrow, or an earlobe that’s hitched slightly differently than the other. Only DNA testing of every organ of your body would show the truth. This depth of testing is improbable and, therefore, you will probably never know if you are one, genetically homogenous body or a mix of twins fused before birth. For further reading: The ABC news story of Lydia Fairchild: http://abcnews.go.com/Primetime/shes-twin/story?id=2315693&page=3 The deal with marmosets: http://www.newscientist.com/article/dn11464-marmosets-may-carry-their-siblings-sex-cells.html#.VELlGEshxg0 And angler fish: http://www.fishbase.org/Summary/FamilySummary.php?Family=Ceratiidae

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