A new strain of mouse is used for determining mutagenic damage caused in vivo by the administration of a known or suspected mutagen. A transgenic mouse, constructed by microinjection of a specially engineered DNA vector into a fertilized mouse egg, carries in the DNA of each of its cells several copies of the injected vector DNA, which is passed on to subsequent generations by normal breeding. The vector DNA carries a target gene for scoring mutations, special DNA sequences permitting the in vitro rescue of the vector from the mouse genomic DNA, and an E. coli origin of replication and ampicillin resistance gene for the selection and propagation of the vector in E. coli. After a mouse has been treated with a possible mutagen, its DNA is isolated from various tissues. The vector DNA is rescued from the genomic DNA and introduced into E. coli where mutations in the target gene can be detected and quantitated.
