Embryonic stem cell culture and gene targeting in transgenic mice

Genetically altered embryonic stem (ES) cells re-injected into mouse blastocysts take part in the formation of all tissues, including the germ line, thus generating transgenic offspring. This approach in combination with the homologous recombination technology offers the possibility of altering ES cells in a controlled manner and therefore of generating transgenic mice with a predetermined genome. We summarize here advances in mouse embryology and genetics that have led to this exciting development.