Sign Up For The TestTube Newsletter Here
Related on TestTube:
Can This DNA Hack Keep You Young Forever?
What You Didn't Know About Your DNA
In Greek mythology, a Chimera is a fire-breathing monster with the head of a lion, the body of a goat, and the tail of a snake. Scientifically speaking, a chimera is someone who has multiple sets of DNA. If every person has a unique DNA signature, then a chimera would be two people rolled into one, and this is actually kind of what's happening. This can occur in utero when an embryo takes in its twin's cells, and therefore genetic material. Identical twins happen when a zygote splits. The moment the zygote splits is extremely important because the later the zygote separation occurs, the more genetic material the two fetuses can share. Two fetuses that don't entirely split can become conjoined twins. If one dies, it's the same thing as losing a pregnancy early, while the remaining baby can be healthy.
It's twin death in the first trimester that scientists are particularly interested in. When one twin dies, its material is sometimes absorbed into the surviving embryo causing what is known as tetragametic chimerism. This is more commonly known as Vanishing Twin Syndrome. The surviving embryo will develop with both its own and its twin's DNA, meaning the child will effectively be born its own twin. Vanishing Twin syndrome is way more common that you might think: In 1945, Dr. Stoeckel was the first to suggest that the rate of multiple conceptions was greater than multiple birth rates. Therefore more zygotes divide than grow into fully formed twins and the dead twin material is reabsorbed by the living twin without a trace--unless the surviving twin's DNA is studied. It's estimated that about one in every eight single childbirths start as multiple pregnancies with cells from the miscarried sibling occasionally absorbed by the survivor.
There are some really interesting implications with chimerism: In 2015, for example, a U.S. man failed a paternity test, though he did seem to be his son's uncle. Doctors found that the DNA in his sperm was different than the DNA in his saliva. His vanished twin had fathered his child. In 2005, American cyclist Tyler Hamilton used tetragametic chimerism as a defense against positive blood doping results, claiming the positive doping test was false because it was actually his vanished twin's blood.
While this is may seem a little creepy, but it's ramifications on DNA testing are fascinating. What do you think about the possibility of being your own twin? Let us know in the comments below.
Human chimera': Man fails paternity test because genes in his saliva are different to those in sperm (Independent)
"The 34-year-old man is the first ever reported case of a paternity test being fooled by a human chimera, someone with extra genes absorbed from a twin lost in early pregnancy."
Vanishing Twin Syndrome: Causes, Signs And Effects (American Pregnancy)
"Vanishing twin syndrome was first recognized in 1945. This occurs when a twin or multiple disappears in the uterus during pregnancy as a result of a miscarriage of one twin or multiple. The fetal tissue is absorbed by the other twin, multiple, placenta or the mother."