[Transgenic animals generation. Regulation of gene expression].

Transgenic animals are organisms with a foreign gene incorporated into their genome, and their development was one of the most important advances in biotechnology. Although knockout animals have already been developed twenty years ago and being transgenic mice generation quite routine, many health care providers still do not understand their impact on biomedical research and their capability of improving human health. In this article, I present the most relevant approaches to generate transgenic animals and discuss how specific genes can be activated or inactivated in a living animal.