ABSTRACT
Genetic mosaicism has been encountered in pigs, sheep and goats. The generation of transgenic animals seems particularly liable to favour the apparition of genetic mosaics at high frequencies. A number of studies using transgenic mice have aimed to evaluate the frequency of mosaicism among founders. In the case of transgenic mice and other mammalian systems, most commonly a linear transgene is microinjected into the pronuclei of fertilized eggs. To obtain a picture of transgene integration process in microinjected mouse embryos, we have used fluorescence in situ hybridization to examine the status of a transgene in the developing microinjected egg. Mosaicism is an issue during basic studies involving small transgenic animals. However, the generation of genetic mosaic founders could be an obstacle in applied uses of transgenic animals for agricultural or pharmaceutical purposes, as for example, animal production improvement, the production of recombinant proteins in milk, transgenic animals for xenografts.
