These mice possess a disrupted human placental alkaline phosphatase (ALPP) transgene inserted into the Gt(ROSA)26Sor locus. Expression of the ALPP transgene is contingent upon Flp-mediated excision of the FRT-flanked STOP cassette placed between the ALPP peptide encoding sequence and the Gt(ROSA)26Sor promoter. This mutant strain serves as a reporter strain, with successful Flp recombinase-mediated excision indicated by ALPP activity. Mice that are homozygous for this allele are viable, fertile, normal in size and do not display any gross physical or behavioral abnormalities. When bred to a strain with broad expression of FLP1 recombinase (see Stock No. 003946 for example), this mutant mouse strain may be useful as an indicator strain for marking most cells in the developing and adult mouse. The Jackson Laboratory 2024, used with permission.