The rate of fraternal twins has been steadily increasing due to rising use of assisted reproductive technologies and fertility treatments. Some researchers speculate that chimerism in humans occurs as often as instances of fraternal, or non-identical, twins. Documented cases of chimerism in humans like Fairchild and Keegan are rare, and the actual incidence rate is unknown. Fairchild matched that pattern, having one set of DNA throughout most of the cells in her body, and another distinct set of DNA in her cervical tissue. But in other chimeras, there is a dominant set of DNA in the body, with the other set only present in certain tissues. In Keegan’s case, her two different sets of DNA were found in cells throughout her body.
#GENETIC CHIMERA SKIN#
Human chimerism is rare but is typically marked by certain characteristics, such as two distinct red blood cell lineages or patchy skin pigmentation, though neither Fairchild nor Keegan exhibited those traits showing obvious signs of chimerism. As a consequence, instead of having cells with identical DNA throughout their body, a chimera has different DNA present in different parts of their body so that the DNA in their blood, for example, may not be the same as the DNA in their saliva. However, in some cases, those two fertilized eggs may fuse together during an early stage of development, resulting in a chimera made of two genetically distinct cell lines. In such cases, two different sperm can fertilize two separate eggs released during hyperovulation, creating two genetically distinct fertilized eggs that can develop into non-identical twins.
However, sometimes the ovaries, which are organs in the female body that produce and store eggs, release more than one egg at a time, a phenomenon known as hyperovulation. In human reproduction, one sperm typically fuses with one egg to create a fertilized egg that can develop into a fetus. An organism gets approximately half of its DNA from each of its parents’ gametes, or their sperm and egg cells, which carry DNA from parent to offspring. Most organisms only have one set of DNA, which is present and identical in every cell throughout that organism’s body. Fairchild’s case was one of the first public accounts of chimerism and has been used as an example in subsequent discussions about the validity and reliability of DNA evidence in legal proceedings within the United States.Ĭhimeras are organisms that have two different sets of DNA, or the genetic material that contains instructions for the development and functioning of an organism, present in their bodies. A cervical swab eventually revealed Fairchild’s second distinct cell line, showing that she had not genetically matched her children because she was a chimera. Following evidence from another case of chimerism documented in The New England Journal of Medicine in a woman named Karen Keegan, Fairchild was able to secure legal counsel and establish evidence of her biological maternity. The state accused Fairchild of fraud and filed a lawsuit against her. Researchers later determined that the genetic mismatch was due to chimerism, a condition in which two genetically distinct cell lines are present in one body. In 2002, after applying for government assistance in the state of Washington, Lydia Fairchild was told that her two children were not a genetic match with her and that therefore, biologically, she could not be their mother. The Case of Lydia Fairchild and Her Chimerism (2002)
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