Transgenic stem cells are grown in vitro (Latin: 'in glass') — in laboratory culture dishes or flasks, outside the living organism. This controlled environment allows manipulation, selection, and characterisation of transgenic clones. After in vitro propagation, transgenic stem cells may be injected into blastocysts or used for other in vivo applications. In vivo means within a living organism; the blastocyst is a stage, not a culture environment.