Transgenic Animals

Abstract Transgenesis implies that a foreign deoxyribonucleic acid (DNA) fragment is introduced into the genome of a multicellular organism and transmitted to progeny. Transgenesis, therefore, differs from gene transfer into cultured cells (transfection) or into the somatic cells of a patient (gene therapy). The foreign DNA can integrate randomly in host genome leading to gene addition or in a targeted manner making it possible precise endogenous gene inactivation or replacement. Transgenesis allows transferring genes from any source in a single generation. Transgenesis is, therefore, complementary to spontaneous mutations, which take place at each reproduction cycle or which are experimentally induced by mutagenic compounds or irradiation. These conventional approaches must be followed by appropriate selection of animals. Transgenesis has become an essential tool to study gene function especially in the medical and pharmaceutical fields. Improvements of breeding and food are also in course. Key Concepts: Transgenesis is more precise and more diverse than conventional selection. Transgenesis and conventional selection are complementary. Transgenesis is an essential tool to study gene action and control. Cloning is presently intensively used to generate transgenic farm animals. Stem cells are currently used for random and targeted gene integration. Transposons and lentiviral vectors are highly efficient for random gene integration. Targeted gene integration using double‐strand genomic DNA break provides researchers with exceptionally efficient new tools. Random gene integration is still intensively used despite its technical limits. Conventional targeted gene transfer is limited by its low efficiency. SiRNAs are efficient tools to inhibit gene expression at the mRNA level. The available tools to generate transgenic animals offer the possibility to develop more relevant biological models and to prepare safer food. Targeted gene transfer should greatly improve transgene expression. Animal behaviourists must participate in conservation planning to protect the future of biodiversity.