Targeted modification of the domestic animal genome.

While the technique of homologous recombination, or gene targeting, has led to the generation of transgenic mice of great value to biomedical research, similar approaches are only being developed in other species. With the exception of recent reports on the generation of gene-targeted sheep, the technology in domestic animals is still in its infancy (45). The development of techniques for generating large animals with deleted or modified genes will result in the generation of animals of great value to society. While the technical difficulties to achieve gene targeting in domestic species are significant, they are not insurmountable. Potential applications in both the bovine and porcine species are described with particular emphasis on the generation of cattle resistant to bovine spongiform encephalopathy (BSE) and pigs that can be of use in xenotransplantation.