WEBVTT - BrainStuff Classics: How Can You Be Your Own Twin?

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<v Speaker 1>Welcome to brain Stuff production of I Heart Radio. Hey

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<v Speaker 1>brain Stuff Lauren Vogelbaum here with a classic brain Stuff episode. Today,

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<v Speaker 1>we're looking at a number of conditions in which different

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<v Speaker 1>cells in a person's body might be operating using a

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<v Speaker 1>different person's DNA, including one in which you can be

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<v Speaker 1>your own twin. Hey brain Stuff, Lauren vogel bam Here.

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<v Speaker 1>Gwen Taylor Mall, a California based singer, asked a doctor

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<v Speaker 1>to investigate the birthmark that stretched across the whole left

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<v Speaker 1>side of her torso. She wondered what role the ruddy

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<v Speaker 1>patch might play, if any, in a series of seemingly

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<v Speaker 1>disparate health conditions she had experienced for most of her life.

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<v Speaker 1>Mole says, everything on the left side of my body

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<v Speaker 1>is slightly larger than the right side. I have a

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<v Speaker 1>double tooth in the left side of my mouth, and

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<v Speaker 1>many sensitivities and allergies to foods, medications, supplements, jewelry, and

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<v Speaker 1>insect bites. While Mole says she hoped for answers, she

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<v Speaker 1>was shocked by what the doctor told her. Her birthmark

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<v Speaker 1>wasn't a birthmark at all. She actually carried the genetic

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<v Speaker 1>code of her twin a sister Mall had absorbed while

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<v Speaker 1>still in the womb. Mal is a chimera, someone who

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<v Speaker 1>carries two distinct sets of DNA, each with the genetic

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<v Speaker 1>code to make a completely separate person. The difference in

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<v Speaker 1>skin pigmentation on Mall's abdomen, these sized discrepancies between her

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<v Speaker 1>left and right sides, and a host of autoimmune symptoms

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<v Speaker 1>are caused by two warring sets of DNA. In Greek mythology,

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<v Speaker 1>a chimera is a fire breathing female monster that's part lion,

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<v Speaker 1>part goat, and part dragon. As remarkable as this creature sounds,

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<v Speaker 1>real life chimeras are perhaps even more astounding and probably

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<v Speaker 1>more common than we realize. Mall's condition, tetracomedic chimerism is

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<v Speaker 1>the most rare of all types of chimerism. It occurs

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<v Speaker 1>when two separate eggs or ova, are each fertilized by

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<v Speaker 1>a separate sperm. Then the fertilized eggs, called zygoats, fused

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<v Speaker 1>together to create a single organism with two genetically distinct

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<v Speaker 1>types of DNA. As the embryo cells multiply and grow,

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<v Speaker 1>so do the two different types of genetic material. The

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<v Speaker 1>result is a baby who is born a chimera. Often,

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<v Speaker 1>baby is born with chimerism have patchy skin or eye pigmentation,

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<v Speaker 1>and sometimes they carry two distinct types of red blood cells. Occasionally,

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<v Speaker 1>chimeras are born with ambiguous genitalia or possessing attributes of

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<v Speaker 1>both male and female sex organs. These symptoms can occur

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<v Speaker 1>not only in humans, but in other types of mammals,

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<v Speaker 1>including mice. Chimerism was once believed to be extremely rare,

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<v Speaker 1>but such conditions are commoner than we realized, as Linda Randolph,

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<v Speaker 1>m d. Told The New York Times. Randolph is a

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<v Speaker 1>pediatrician at Children's Hospital in Los Angeles, an author of

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<v Speaker 1>a chimerism review published in the American Journal of Medical Genetics.

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<v Speaker 1>In addition to genetic chimerism, the condition is commonly caused

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<v Speaker 1>when another genetic code is introduced to the body by

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<v Speaker 1>organ or tissue transplants, as well as by blood transfusions.

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<v Speaker 1>For example, when someone undergoes a bone marrow transplant, they'll

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<v Speaker 1>carry blood cells that are identical to their donor for

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<v Speaker 1>the rest of their lives, in addition to their own

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<v Speaker 1>genetically distinct blood cells. A blood transfusion, however, only produces

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<v Speaker 1>a temporary chimera. Condition, The donor blood cells will live

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<v Speaker 1>about a hundred and fifteen days in the host's body

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<v Speaker 1>and will eventually be completely replaced by red blood cells

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<v Speaker 1>carrying their original genetic code. These types of chimerism are

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<v Speaker 1>commonly known as microchimerism, and one of the most frequent

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<v Speaker 1>causes is pregnancy. Trace fetal stem cells often remain in

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<v Speaker 1>a mother long after she has given birth. Some of

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<v Speaker 1>these stem cells have even been found to reside in

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<v Speaker 1>women's brains. Likewise, a pregnant woman's cells can cross the

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<v Speaker 1>placenta and become part of their child's liver, heart, thymus, gland,

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<v Speaker 1>and bloodstream. Many people may not ever suspect that microchimerism

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<v Speaker 1>is part and parcel of their existence, but it's probably

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<v Speaker 1>more frequent than we realize. In fact, chimerism, both tetragametic

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<v Speaker 1>and micro may someday challenge how medicine, forensics, and even

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<v Speaker 1>the legal system contend with DNA. DNA testing, which is

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<v Speaker 1>done by collecting small amounts of human saliva, semen, hair, bone, blood,

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<v Speaker 1>or skin tissue, relies on the notion that every cell

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<v Speaker 1>in an individual body contains identical DNA, and that each

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<v Speaker 1>person has different DNA chimerism challenges the notion of a

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<v Speaker 1>one DNA to one person system. In one complex assault case,

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<v Speaker 1>for example, evidence at the scene matched a DNA blood

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<v Speaker 1>sample from a criminal already profiled in a law enforcement database. However,

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<v Speaker 1>this person was in jail when the assault occurred. To

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<v Speaker 1>make matters even more confusing, the DNA blood sample also

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<v Speaker 1>matched the DNA profile of another person who could also

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<v Speaker 1>have been implicated in the crime. After investigating, it was

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<v Speaker 1>determined that the two men were brothers. The man in

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<v Speaker 1>jail had previously received a bone marrow transplant from his brother.

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<v Speaker 1>This means that the jailed man was a chimera. His

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<v Speaker 1>blood DNA profile matched that of his brother's blood DNA,

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<v Speaker 1>while his saliva DNA profile was distinctly his own. In

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<v Speaker 1>the end, investigators used a blood sample and cheek swab

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<v Speaker 1>to make a d n A match from the crime

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<v Speaker 1>scene and charged the correct brother with the crime. Today's

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<v Speaker 1>episode is based on the article calimerism you Can be

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<v Speaker 1>your Own twin on how stuff Works dot Com, written

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<v Speaker 1>by Laur L. Dove. Brain Stuff is production of I

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<v Speaker 1>Heart Radio in partnership with how stuff works dot Com,

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<v Speaker 1>and it is produced by Tyler Clang four more podcasts

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<v Speaker 1>from my heart Radio. Visit the i heart Radio app,

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<v Speaker 1>Apple podcasts, or wherever you listen to your favorite shows.