![]() Some cells come from sperm 1 and egg 1, while the rest come from sperm 2 and egg 2. Because eggs and semen are known as gametes, and since four of them end up creating a single person, scientists have called this phenomenon “tetragametic chimerism.” More poetically, it has been referred to as “the vanishing twin.”Ī tetragametic chimera thus has two main types of cells making up their body. Sometimes, though, these twins fuse in the womb and become one. DNA from each twin can thus be exchanged, and these siblings end up with parts of each other.Īnother natural way that genetic chimeras can emerge is when two eggs get fertilized by two sperms at the same time, which would normally result in fraternal twins. In medical terms, this cross-connection is known as an anastomosis. When twins are growing in the womb, the blood vessels feeding them can connect. But there are interesting cases where the developing embryo becomes a sort of chimera. It divides into two, making copies of these chromosomes, and we think that every cell down the line ends up with the same genetic bundle. Sperm meets egg, and we get a zygote with a full set of chromosomes. ![]() We assume that we have a single genetic code in all of our cells, one born of the combination of one half of our father’s DNA and one half of our mother’s DNA. pointed that out in a somewhat flamboyant fashion by having its criminal proclaim that, “I’m a creature of myth.” He was a chimera, though not the sort with a fire-breathing head. The season 4 finale of the television show C.S.I. She was a monstrous creature, a hybrid of many animals, ultimately slayed by the hero Bellerophon.īut chimeras do exist outside of Greek myths. “She was in the fore part a lion, in the hinder a serpent, and in the midst a goat, breathing forth in terrible wise the might of blazing fire.” This is how Homer, in his famous tale The Iliad, describes the Chimera. To solve this puzzling case, we need to appreciate mythical beasts. How had he escaped, committed the crime, and returned to jail undetected?ĭNA may not lie, but we have to understand its rare eccentricities. Case closed, right?Įxcept that when the sexual assault took place, this known criminal was behind bars. ![]() When the extracted DNA is compared to the criminal justice DNA database, a match is found to a blood sample that was taken from a known criminal. The evidence they have is sperm, which famously contains DNA. A serious sexual assault has been committed and investigators are trying to find out who the perpetrator is.
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