Chimera from Latin chimaera
, from the Greek chimaira
From the days of Greek mythology, the chimera (pronounced "kih-MEE-ra") was a combination of several animals - it had the head of a lion, the body of a she-goat, and the tail of a serpent (dragon). Some stories include the head of each, and the goat head could breath fire. The Chimera was the child of Typhon (a giant) and Echidna (half human female, half snake), and raised by Amisodarus. The siblings of the Chimera were Cerberus, the Hydra, and Orthrus.
As part of a complicated betrayal and false accusation that is common in Greek mythology (the treacherous woman type), Bellerophon was sent the kingdom of Lycia to be killed by the king. Instead, the king sent him off to kill the Chimera with the hope that Bellerophon would be killed instead. Instead, Bellerophon rode Pegasus (as directed by Polyidus, a soothsayer) and killed it with a lump of lead on the end of a spear stuck in its mouth after weakening it with an arrow. The lead melted from the firey breath and ran down the throat and hardened, killing the Chimera.
In the days of Gothic architecture, the chimera was a type of gargoyle that combined several different animals into one body. These often took the forms from mythology that was abundant with mixes of humans and animals in a body. These ranged from the sphinx (a human head on a lion's body) to that of mermaids, centaurs, and the Chimera itself.
In today's world of science and biology, the chimera is an organism composed of tissues that are genetically different.
The oldest form of creation of chimeras is from botany where a branch of one plant is grafted into the trunk of another. This is the process used to produce seedless fruits. These fruits are formed from a mutation or selective breeding to not have any seeds and thus are infertile themselves. The only way to make another tree (or rather branch of a tree) has been to form a chimera.
Chimeras have existed in animal biology for some time, though it wasn't until the advances in embryo development that the word became popularized. Any being that has had a transplant from another is technically a chimera... heart, lung, kidney, or bone barrow. The essence of the chimera is that the organism consists of multiple tissues from different genetic backgrounds.
Within animals, chimeras naturally exist when there is a mutation in one or more cells of a developing embryo (this is also true for plants and is often seen in tabacco). From this, the organism will have two sets of cells that have different DNA. The chimera can also be formed by artifically implanting cells from one organism into the embryo of another. The most common example of this is the geep which was produced by injecting the goat inner cell mass into a sheep blastocyst.
This is different than a hybrid where two related species (such as the lion and tiger, or horse and donkey) mate to form an infertile offspring (such as the liger or tigron and mule).