Chimera

Chimera refers to a single organism composed of cells with more than one distinct genotype. In biology, this means an individual derived from two or more zygotes, which can include possessing blood cells of different blood types, or subtle variations in form. The term is derived from the Chimera of Greek mythology, a monstrous creature that was part fire-breathing lion, part goat, and part snake.

Etymology

The word "chimera" comes from the Greek mythology, where Chimera was a monstrous creature described as part lion, part goat, and part snake. Over time, the term has come to describe any mythical or fictional animal with parts taken from various animals, or, more generally, anything composed of very disparate parts.

Biological Chimeras

In genetics, chimeras are formed from at least two different genetic cell lines originating from different zygotes. This can occur naturally or be induced artificially. Natural chimerism can occur in human twins where cells from one twin are incorporated into the other. Artificial chimerism can be induced by transplanting bone marrow from one individual to another, effectively changing the recipient's blood type to that of the donor.

Types of Chimerism

• Microchimerism: Occurs when a small number of cells from one individual are incorporated into another. This often occurs naturally during pregnancy, where cells from the fetus cross into the mother and vice versa.
• Tetragametic chimerism: This type occurs when two eggs are fertilized by two different sperm cells and then fuse together, forming a single organism with two different sets of DNA.

Applications and Implications

Chimerism has important implications in medicine, particularly in the fields of transplantation and genetic research. In transplantation, understanding chimerism is crucial for the success of organ transplants, particularly bone marrow transplants. In genetic research, chimeras can be used to study gene function and disease development.

Legal and Ethical Considerations

The existence of chimeras raises several ethical and legal issues, particularly concerning identity and human rights. The legal identity of individuals with more than one set of DNA can be complex, especially in cases of criminal investigations.

In Popular Culture

Chimeras often appear in various forms of literature and media, typically as creatures composed of parts from various animals. They symbolize the blurring of natural boundaries and are often used to explore themes of identity and transformation.