The TSG-p53® mouse was developed in the laboratory of Lawrence A. Donehower and Allan Bradley at the Baylor College of Medicine. The model was created by targeting the Trp53 gene in AB1 ES cells and injecting the targeted cells into C57BL/6 blastocysts. Resultant chimeras were backcrossed to C57BL/6J for two generations (N2). Taconic received stock in 1991. The mice were backcrossed to N3 for caesarean derivation and to N4 immediately after derivation. In 1995, backcrossing of the N4 heterozygote to C57BL/6NTac mice recommenced at Taconic and continued to twelve generations (N12). The line was embryo transfer derived in 1998. Heterozygous and homozygous mice are maintained at N12 through mating of homozygous male mice with heterozygous females.