The chimera from Greek mythology is a fire-breathing monster with a lion’s head, a goat’s body, and a serpent’s tail. The chimera of biotechnology is an animal formed from two different species or strains—that is, a mixture of cells from two very early embryos. Most chimeras used in research are made from different mouse strains—and they cannot reproduce.

Recombinant DNA is hybrid DNA that has been created from more than one source. For example, the splicing of human DNA into bacterial DNA so that a human gene product is produced by a bacterial cell results in recombinant DNA.