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Speaker 1: Welcome to brain Stuff from How Stuff Works, Hey, brain Stuff,

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Speaker 1: Lauren Vogel bam here. When Taylor Mall, a California based singer,

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Speaker 1: asked a doctor to investigate the birthmark that stretched across

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Speaker 1: the whole left side of her torso, she wondered what

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Speaker 1: role the ruddy patch might play, if any, in a

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Speaker 1: series of seemingly disparate health conditions she had experienced for

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Speaker 1: most of her life. Mole says, everything on the left

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Speaker 1: side of my body is slightly larger than the right side.

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Speaker 1: I have a double tooth in the left side of

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Speaker 1: my mouth, and many sensitivities and allergies to foods, medications, supplements, jewelry,

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Speaker 1: and insect bites. While Mall says she hoped for answers,

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Speaker 1: she was shocked by what the doctor told her. Her

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Speaker 1: birthmark wasn't a birthmark at all. She actually carried the

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Speaker 1: genetic code of her twin, a sister Moll had absorbed

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Speaker 1: while still in the womb. Mall is a kind mira,

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Speaker 1: someone who carries two distinct sets of DNA, each with

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Speaker 1: the genetic code to make a completely separate person. The

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Speaker 1: difference in in pigmentation on Mall's abdomen. These sized discrepancies

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Speaker 1: between her left and right sides, and a host of

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Speaker 1: autoimmune symptoms are caused by two warring sets of DNA.

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Speaker 1: In Greek mythology, a chimera is a fire breathing female

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Speaker 1: monster that's part lion, part goat, and part dragon. As

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Speaker 1: remarkable as this creature sounds, real life chimeras are perhaps

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Speaker 1: even more astounding and probably more common than we realize.

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Speaker 1: Mole's condition. Tetra Amedic chimerism is the most rare of

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Speaker 1: all types of chimerism. It occurs when two separate eggs

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Speaker 1: or ova are each fertilized by a separate sperm. Then

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Speaker 1: the fertilized eggs, called zygoats, fused together to create a

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Speaker 1: single organism with two genetically distinct types of DNA. As

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Speaker 1: the embryo cells multiply and grow, so do the two

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Speaker 1: different types of genetic material. The result is a baby

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Speaker 1: who is born a chimera. Often baby is born with

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Speaker 1: chimerism have patchy skin or eye pigmentation, and sometimes they

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Speaker 1: carry two distinct types of red blood cells. Occasionally, chimeras

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Speaker 1: are born with ambiguous genitalia or possessing attributes of both

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Speaker 1: male and female sex organs. These symptoms can occur not

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Speaker 1: only in humans, but in other types of mammals, including mice.

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Speaker 1: Chimerism was once believed to be extremely rare, but such

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Speaker 1: conditions are commoner than we realized, as Linda Randolph, m d.

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Speaker 1: Told The New York Times. Randolph is a pediatrician at

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Speaker 1: Children's Hospital in Los Angeles an author of a chimerism

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Speaker 1: review published in the American Journal of Medical Genetics. In

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Speaker 1: addition to genetic chimerism, the condition is commonly caused when

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Speaker 1: another genetic code is introduced to the body by organ

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Speaker 1: or tissue transplants, as well as by blood transfusions. For example,

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Speaker 1: when someone undergoes a bone marrow transplant, they'll carry blood

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Speaker 1: cells that are identical to their donor for the rest

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Speaker 1: of their lives, in addition to their own genetically distinct

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Speaker 1: blood cells. Blood transfusion, however, only produces a temporary chimera condition.

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Speaker 1: The donor blood cells will live about a hundred and

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Speaker 1: fifteen days in the host's body and will eventually be

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Speaker 1: completely replaced by red blood cells carrying their original genetic code.

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Speaker 1: These types of chimerism are commonly known as microchimerism, and

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Speaker 1: one of the most frequent causes is pregnancy. Trace Fetal

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Speaker 1: stem cells often remain in a mother long after she

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Speaker 1: has given birth. Some of these stem cells have even

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

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Speaker 1: woman's cells can cross the placenta and become part of

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

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Speaker 1: may not ever suspect that microchimerism is part and parcel

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

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Speaker 1: In fact, chimerism, both tetragamtic and micro may someday challenge

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Speaker 1: how medicine, forensics, and even the legal system contend with DNA.

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Speaker 1: DNA testing, which is done by collecting small amounts of

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Speaker 1: humans aliva, semen, hair, bone, blood, or skin tissue, relies

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Speaker 1: on the notion that every cell in an individual body

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Speaker 1: contains identical DNA, and that each person has different DNA

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Speaker 1: Cimerism challenges the notion of a one DNA to one

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

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Speaker 1: at the scene matched a DNA blood sample from a

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Speaker 1: criminal already profiled in a law enforcement database. However, this

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Speaker 1: person was in jail when the assault occurred. To make

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Speaker 1: matters even more confusing, the DNA blood sample also matched

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Speaker 1: the DNA profile of another person who could also have

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Speaker 1: been implicated in the crime. After investigating, it was determined

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Speaker 1: that the two men were brothers. The man in jail

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Speaker 1: had previously received a bone marrow transplant from his brother.

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Speaker 1: This means that the jailed man was a chimera. His

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Speaker 1: blood DNA profile matched that of his brother's blood DNA,

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Speaker 1: while his saliva DNA profile was distinctly his own. In

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Speaker 1: the end, investigators used a blood sample and cheek swab

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Speaker 1: to make a DNA match from the crime scene and

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Speaker 1: charged the correct brother with the crime. Today's episode was

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Speaker 1: written by Laurie L. Dove and produced by Tyler Klang.

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Speaker 1: For more on this and lots of other multi natured topic,

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Speaker 1: visit our home planet, how Stuff Works dot com. M