Figure 1.

Conventional method of gene disruption by using homologous recombination in embryonic stem (ES) cells. A, Design and construction of a mutant vector transfected into ES cells; those cells carrying the mutation were screened. B, The injection of ES cells carrying the mutation into embryos. The chimeric mice are bred and the heterozygous mice are obtained through germ‐line transmission. The process takes 1‐2 years until completion. drug^r, drug resistance gene; pA, polyadenylation signal; Prom, promoter