EXPERIMENTAL FIGURE 6-40 Transgenic mice are produced by random integration of a foreign gene into the mouse germ line. Foreign DNA injected into one of the two pronuclei (the male and female haploid nuclei contributed by the parents) has a good chance of being randomly integrated into the chromosomes of the diploid zygote. Because a transgene is integrated into the recipient genome by nonhomologous recombination, it does not disrupt endogenous genes. See R. L. Brinster et al., 1981, Cell 27:223.