Transgenic animals are very useful for scientific, pharmaceutical, and agricultural purposes. In livestock, transgenic technology has been used forth genetic alteration of farm animals, the production of human proteins inlarge quantities in the milk of transgenic farm animals (Clark et al., 1989; Ebert et al., 1991; Kimpenfort et al., 1991; Wall et al., 1991; Kimpenfort et al., Well et al,m 1991; Hill et al., 1992; Velander et al., 1994; Chen et al.), and the generation of animals with organs suitable for xenotransplantation (Pinkert, 1994; Chen et al., 1999). (omitted)