WEBVTT - How Can You Be Your Own Twin?

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<v Speaker 1>Welcome to brain Stuff from How Stuff Works, Hey, brain Stuff,

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<v Speaker 1>Lauren Vogel bam here. When Taylor Mall, a California based singer,

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<v Speaker 1>asked a doctor to investigate the birthmark that stretched across

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<v Speaker 1>the whole left side of her torso, she wondered what

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<v Speaker 1>role the ruddy patch might play, if any, in a

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<v Speaker 1>series of seemingly disparate health conditions she had experienced for

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<v Speaker 1>most of her life. Mole says, everything on the left

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<v Speaker 1>side of my body is slightly larger than the right side.

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<v Speaker 1>I have a double tooth in the left side of

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

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

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

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

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<v Speaker 1>genetic code of her twin, a sister Moll had absorbed

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<v Speaker 1>while still in the womb. Mall is a kind mira,

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<v Speaker 1>someone who carries two distinct sets of DNA, each with

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<v Speaker 1>the genetic code to make a completely separate person. The

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<v Speaker 1>difference in in pigmentation on Mall's abdomen. These sized discrepancies

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<v Speaker 1>between her left and right sides, and a host of

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<v Speaker 1>autoimmune symptoms are caused by two warring sets of DNA.

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<v Speaker 1>In Greek mythology, a chimera is a fire breathing female

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<v Speaker 1>monster that's part lion, part goat, and part dragon. As

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<v Speaker 1>remarkable as this creature sounds, real life chimeras are perhaps

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<v Speaker 1>even more astounding and probably more common than we realize.

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<v Speaker 1>Mole's condition. Tetra Amedic chimerism is the most rare of

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<v Speaker 1>all types of chimerism. It occurs when two separate eggs

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<v Speaker 1>or ova are each fertilized by a separate sperm. Then

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<v Speaker 1>the fertilized eggs, called zygoats, fused together to create a

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<v Speaker 1>single organism with two genetically distinct types of DNA. As

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<v Speaker 1>the embryo cells multiply and grow, so do the two

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<v Speaker 1>different types of genetic material. The result is a baby

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

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<v Speaker 1>chimerism have patchy skin or eye pigmentation, and sometimes they

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

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

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<v Speaker 1>male and female sex organs. These symptoms can occur not

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<v Speaker 1>only in humans, but in other types of mammals, including mice.

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<v Speaker 1>Chimerism was once believed to be extremely rare, but such

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<v Speaker 1>conditions are commoner than we realized, as Linda Randolph, m d.

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<v Speaker 1>Told The New York Times. Randolph is a pediatrician at

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<v Speaker 1>Children's Hospital in Los Angeles an author of a chimerism

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

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

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

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

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

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<v Speaker 1>cells that are identical to their donor for the rest

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<v Speaker 1>of their lives, in addition to their own genetically distinct

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<v Speaker 1>blood cells. Blood transfusion, however, only produces a temporary chimera condition.

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<v Speaker 1>The donor blood cells will live about a hundred and

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<v Speaker 1>fifteen days in the host's body and will eventually be

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<v Speaker 1>completely replaced by red blood cells carrying their original genetic code.

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<v Speaker 1>These types of chimerism are commonly known as microchimerism, and

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<v Speaker 1>one of the most frequent causes is pregnancy. Trace Fetal

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<v Speaker 1>stem cells often remain in a mother long after she

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<v Speaker 1>has given birth. Some of these stem cells have even

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<v Speaker 1>been found to reside in women's brains. Likewise, a pregnant

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<v Speaker 1>woman's cells can cross the placenta and become part of

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<v Speaker 1>their child's liver, heart, thymus, gland, and bloodstream. Many people

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<v Speaker 1>may not ever suspect that microchimerism is part and parcel

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<v Speaker 1>of their existence, but it's probably more frequent than we realize.

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<v Speaker 1>In fact, chimerism, both tetragamtic and micro may someday challenge

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<v Speaker 1>how medicine, forensics, and even the legal system contend with DNA.

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<v Speaker 1>DNA testing, which is done by collecting small amounts of

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<v Speaker 1>humans aliva, semen, hair, bone, blood, or skin tissue, relies

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<v Speaker 1>on the notion that every cell in an individual body

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<v Speaker 1>contains identical DNA, and that each person has different DNA

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<v Speaker 1>Cimerism challenges the notion of a one DNA to one

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<v Speaker 1>person's system. In one complex assault case, for example, evidence

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<v Speaker 1>at the scene matched a DNA blood sample from a

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

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

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

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

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

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

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<v Speaker 1>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 DNA match from the crime scene and

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<v Speaker 1>charged the correct brother with the crime. Today's episode was

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<v Speaker 1>written by Laurie L. Dove and produced by Tyler Klang.

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<v Speaker 1>For more on this and lots of other multi natured topic,

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<v Speaker 1>visit our home planet, how Stuff Works dot com. M