Chimeric parents

During a child support dispute in 2002, a DNA test seemed to show that a mother was not the parent of her own biological children. The truth was stranger than anyone expected.

Chimeric lime
HeberM, CC BY-SA 3.0, via Wikimedia Commons

Back in 2002, a woman named Lydia Fairchild was in a Washington state court for a child support dispute. Part of the process was a routine DNA test to establish that the other party was the genetic father of her children. The results were a real puzzle: her ex-partner was certainly the father, but somehow she was not the mother.

This must have come as quite a shock to Fairchild: she knew the children were hers because she had given birth to them all. And she knew there had been no in vitro fertilisation, no way that the eggs were not hers. The court suspected shenanigans. Some kind of scam, perhaps? A secret surrogacy agreement gone wrong? But the truth of the matter was far stranger.

The Classical chimera is a monster with the head of a lion, the body of a goat, and the rear end of a snake. It’s one of many rather uncreative mythological creatures that are just animal body parts mashed together: the manticore (human / lion / porcupine), the griffin (lion / eagle), the lamassu (lion / eagle / bull / human), and so on. The word “chimera” has come to mean a kind of random mash-up. Today it’s used for a rather rare genetic phenomenon: a plant or animal which has more than one set of DNA.

The picture at the top of this post is a chimera. The two halves of this citrus fruit have two distinct and separate genetic sequences. This can be the result of mutation, but it can also occur when two embryos fuse together at a very early stage of development. Essentially, twins merge together and becoming one, but both still keep their DNA.

Human chimeras are rare, but possible. The choice of name is unfortunate – chimeras are not monsters. It’s just another fascinating branch of the spectrum of human genetics. And, as her lawyer miraculously deduced, Lydia Fairchild was a chimera.

It all depended on where the DNA sample came from. Fairchild’s hair and skin had one set of DNA, but a swab from her cervix showed a completely different set of genes… and those were the genes passed on to her children. In other words, she had two sets of genes and they were testing the wrong ones. The mystery was solved and Fairchild exonerated. They were her children after all.

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