In Greek mythology, a chimera is a female creature made up of three different animals. In reality, chimerism is no where near as mystical; it is simply characterized by one organism made up of at least two different genotypes - or two separate sets of genes. Animals can be chimeras, like an anglerfish during procreation. Or, like a cat with a perfectly halved face.
But can people be chimeras? Yes, but it is sometimes not as obvious as it is with the rest of the animal kingdom. Humans classified as chimeras have two different sets of DNA or blood types. Genetically, a chimera is exemplified as a person who was meant to be born in a set of twins but absorbed the other fetus in the womb. Individuals who are chimeras can suffer devastating effects legally and physically due to their mixed genetic makeup.
Taylor Muhl sought out the opinion of a doctor after noticing a reddish "birthmark" covering the left half of her torso. She also noticed that everything on that side of her body was larger or had sensitivities or allergies not present on the right side.
The doctor diagnosed Muhl with tetragametic chimerism, which occurs when two eggs are fertilized by two different sperm and then one of them absorbs the other. The result in this case is two blood types, two immune systems, and two skin colors on the torso.
When applying for benefits for herself and her children, Lydia Fairchild had to provide a DNA sample from herself and her brood to prove they were related. The tests came back showing that Fairchild could not be the biological mother of her children.
Even after witnessing Fairchild give birth, the state intervened since the DNA proved the kids were not her own. In fact, the DNA tests revealed that her twin sister was actually the biological mother of her children - except Fairchild did not have a twin.
After learning about another woman that had two different DNA types in her body, it was concluded that Fairchild was actually her own twin due to chimerism. Further testing was done and Fairchild was finally proven to be the biological mother of her children.
A man and his partner underwent fertility treatments to have their son. However, after the child was born, blood work revealed the child was not related to the father. The parents had the child's DNA tested, and the test revealed the child only shared 10% of his father's DNA. Naturally, the couple began to wonder if the fertility clinic had made a mistake. Additional testing showed that the father was a chimera; the DNA in his body was 90% his own, while the other 10% was actually from his unborn fraternal twin.
As Time reported in 2015: "Apparently, the father had absorbed some of his twin's cells in the womb, effectively becoming a blend, or chimera, of himself and his brother." Geneticist Barry Starr said, "He is like dad and uncle to his kids."
Vanishing twin syndrome is the cause of most known cases of chimerism. According to the American Pregnancy Association, vanishing twin syndrome happens when "a twin or multiple disappears in the uterus during pregnancy as a result of the miscarriage of one twin or multiple. The fetal tissue is absorbed by the other twin, multiple, placenta, or the mother."
If a female twin absorbs her twin in the womb, or vice-versa, the resulting chimera can possess both sets of female organs. In one case, a woman conceived by in vitro fertilization implanted three fertilized eggs into her womb; only one baby was born.
Her son appeared to have normal male genitalia, but surgical exploration would reveal an ovary, a fallopian tube, and part of a uterus in his body. After their removal, he was able to continue to grow with no further female genitalia appearing.