Chimera & Mosaicism

Topics: Gene, In vitro fertilisation, Genetics Pages: 5 (2038 words) Published: April 17, 2007
Chimera according to the genome glossary is an organism which possesses cells or tissues with a different genotype. This can be caused due to mutated cells of the host organism or cells from a different organism or species. ( Mosaicism - the condition in which an organism has two or more cell populations that differ in genetic makeup condition - a mode of being or form of existence of a person or thing; "the human condition" (encyclopedia "In medicine (genetics), a mosaic or mosaicism denotes the presence of two populations of cells with different genotypes in one individual, who has developed from a single fertilized egg. Mosaicism may result from a mutation during development, which is propagated to only a subset of the adult cells. Although the two can have some common symptoms, mosaicism is distinctly different from chimerism. In chimerism, the two or more genotypes arise from more than one zygote, while in mosaics; these genotypes arise from only a single cell. Sometimes intersex conditions can be caused by mosaicism - where some cells in the body have XX and others XY chromosomes." (

In Greek mythology, the original "Chimera" (pronounced as kih-MEE-ra, and the adjective form "chimerical" pronounced as kih-MER-ih-cal) was a fire-breathing female monster with the head of a lion, the body of a goat and the hindquarters of a dragon. The terrifying Chimera may have merely been a product of a substandard family environment -- her father was the giant Typhon, her mother the half-serpent Echidna. Her siblings were the Cerebrus (the three-headed hound who eventually found work guarding the gates of Hell), Hydra (a nine-headed aquatic monster) and Orthrus (the runt of the litter, a prosaic two-headed dog). As per the mythology, Chimera pounced around making everyone wretched until one day a man named Bellerophon, riding on the winged horse Pegasus slays her.( Thought to be a myth, it was found that cases of Chimera actually existed in humans when certain criminal cases erupted. One such case was when a woman has been raped by a man and the women claimed a particular man was the culprit. However, authorities had found it difficult to convict the suspect. It so happened that the DNA taken women did not match the DNA of the man. After extensive investigation the women's statements revealed it to be same person being responsible for the crime. When another series of DNA tests were taken from the suspect, this time from his hair it was found that the DNA sample matched. Those people who have two different types of DNA in their body are called chimeras after the mythological creature with a head of lion, body of a goat and a tail of a serpent. These people can also be called mosaics. It has found that these people have two different types of DNA in different parts of their body. Though very rare, this could have been due to various reasons. ( The most common reason that chimeras are formed if developing fraternal twin embryos join together to become one embryo. This is different from identical twins that are formed when a single embryo splits into two. This occurrence takes place in the very early stages of the embryo development , so when it develops the baby that is born is healthy but with two types of DNAs. Another reason for chimeras to form is when developing fraternal twin share the same blood supply. This happens when the twins with different DNA share a placenta and cells from their blood mix together. This results in the twins being chimeras. Chimeras are also formed through mistakes or mutations taking place in the division of the cells in the development embryo. This mainly takes place when the cells split into two so that they are able to be formed into more of themselves for the...

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