A technique for inserting into laboratory mice genetic loci modified in desired ways. Standard recombinant DNA techniques are used to introduce desired chemical changes into cloned DNA sequences of a chosen locus. The mutated sequence is then transferred into an embryo-derived, stem-cell genome, where it is allowed to undergo homologous recombination (q.v.). Microinjection of mutant stem cells into mouse blastocysts is then performed to generate chimeras. The stem cells come from a black mouse line, and the recipient embryos are from a white strain. Therefore, chimeras can be identified by their variegated coat colors. Large numbers of these chimeras are mated together, and in the F1 rare black progeny are observed. Some of these will be homozygous for the targeted gene. If the mutation represents a null allele (q.v.), the functions of the normal allele can be inferred from the abnormal phenotypes shown by the homozygotes. See Chronology, 1988, Mansour et al.; knockout.
Subjects: Genetics and Genomics.