In Greek mythology, a chimera is a fire-breathing monster that has a goat’s body, a lion’s head and the tail of a serpent. While the Greek chimera is just a myth, you can actually find a human chimera in real life. Every woman who has ever been pregnant possesses the DNA of every child she has ever conceived.
Microchimerism happens to all pregnant women. Currently, scientists believe that up to 10 percent of the free-floating DNA in a pregnant woman’s bloodstream is from the fetus. Even though this rate falls after birth, it can persist for decades afterward.
In 1996, a geneticist named Diana Bianchi from Tufts Medical Center discovered that a mother had male fetal cells in her bloodstream 27 years after she originally gave birth. As mothers have additional children, the foreign material becomes more complex. The DNA from older children can actually transfer through the mother to younger siblings.
Mothers are more than just chimeras though. There is now evidence that these fetal cells may influence whether a woman develops cancer, rheumatoid arthritis and lupus. Scientists have found these fetal cells in the spleens of women who had systemic sclerosis. For cancer, fetal cells seem to be capable of sometimes reducing cancer risk and sometimes increasing the risk of developing cancer. Scientists even think that fetal cells may help the body’s immune system become better at detecting cancel cells later on.
Scientists are still working to understand all of the ways fetal DNA affects the mother’s health. They are also just beginning to study the ways that the mother’s DNA can impact the fetus. In the meantime, the story of the human chimera will remain just as amazing and astounding as the stories in ancient myths.