Welcome to brain Stuff production of I Heart Radio. Hey brain Stuff Lauren Vogelbaum here with a classic brain Stuff episode. Today, we're looking at a number of conditions in which different cells in a person's body might be operating using a different person's DNA, including one in which you can be your own twin. Hey brain Stuff, Lauren vogel bam Here. Gwen Taylor Mall, a California based singer, asked a doctor to investigate the birthmark that stretched across the whole left
side of her torso. She wondered what role the ruddy patch might play, if any, in a series of seemingly disparate health conditions she had experienced for most of her life. Mole says, everything on the left side of my body is slightly larger than the right side. I have a double tooth in the left side of my mouth, and many sensitivities and allergies to foods, medications, supplements, jewelry, and insect bites. While Mole says she hoped for answers, she
was shocked by what the doctor told her. Her birthmark wasn't a birthmark at all. She actually carried the genetic code of her twin a sister Mall had absorbed while still in the womb. Mal is a chimera, someone who carries two distinct sets of DNA, each with the genetic code to make a completely separate person. The difference in skin pigmentation on Mall's abdomen, these sized discrepancies between her left and right sides, and a host of autoimmune symptoms
are caused by two warring sets of DNA. In Greek mythology, a chimera is a fire breathing female monster that's part lion, part goat, and part dragon. As remarkable as this creature sounds, real life chimeras are perhaps even more astounding and probably more common than we realize. Mall's condition, tetracomedic chimerism is the most rare of all types of chimerism. It occurs when two separate eggs or ova, are each fertilized by
a separate sperm. Then the fertilized eggs, called zygoats, fused together to create a single organism with two genetically distinct types of DNA. As the embryo cells multiply and grow, so do the two different types of genetic material. The result is a baby who is born a chimera. Often, baby is born with chimerism have patchy skin or eye pigmentation,
and sometimes they carry two distinct types of red blood cells. Occasionally, chimeras are born with ambiguous genitalia or possessing attributes of both male and female sex organs. These symptoms can occur not only in humans, but in other types of mammals, including mice. Chimerism was once believed to be extremely rare, but such conditions are commoner than we realized, as Linda Randolph,
m d. Told The New York Times. Randolph is a pediatrician at Children's Hospital in Los Angeles, an author of a chimerism review published in the American Journal of Medical Genetics. In addition to genetic chimerism, the condition is commonly caused when another genetic code is introduced to the body by organ or tissue transplants, as well as by blood transfusions.
For example, when someone undergoes a bone marrow transplant, they'll carry blood cells that are identical to their donor for the rest of their lives, in addition to their own genetically distinct blood cells. A blood transfusion, however, only produces a temporary chimera. Condition, The donor blood cells will live about a hundred and fifteen days in the host's body and will eventually be completely replaced by red blood cells
carrying their original genetic code. These types of chimerism are commonly known as microchimerism, and one of the most frequent causes is pregnancy. Trace fetal stem cells often remain in a mother long after she has given birth. Some of these stem cells have even been found to reside in women's brains. Likewise, a pregnant woman's cells can cross the placenta and become part of their child's liver, heart, thymus, gland,
and bloodstream. Many people may not ever suspect that microchimerism is part and parcel of their existence, but it's probably more frequent than we realize. In fact, chimerism, both tetragametic and micro may someday challenge how medicine, forensics, and even
the legal system contend with DNA. DNA testing, which is done by collecting small amounts of human saliva, semen, hair, bone, blood, or skin tissue, relies on the notion that every cell in an individual body contains identical DNA, and that each person has different DNA chimerism challenges the notion of a one DNA to one person system. In one complex assault case, for example, evidence at the scene matched a DNA blood
sample from a criminal already profiled in a law enforcement database. However, this person was in jail when the assault occurred. To make matters even more confusing, the DNA blood sample also matched the DNA profile of another person who could also have been implicated in the crime. After investigating, it was determined that the two men were brothers. The man in jail had previously received a bone marrow transplant from his brother.
This means that the jailed man was a chimera. His blood DNA profile matched that of his brother's blood DNA, while his saliva DNA profile was distinctly his own. In the end, investigators used a blood sample and cheek swab to make a d n A match from the crime scene and charged the correct brother with the crime. Today's episode is based on the article calimerism you Can be your Own twin on how stuff Works dot Com, written
by Laur L. Dove. Brain Stuff is production of I Heart Radio in partnership with how stuff works dot Com, and it is produced by Tyler Clang four more podcasts from my heart Radio. Visit the i heart Radio app, Apple podcasts, or wherever you listen to your favorite shows.