The mutant-specific SR-PCR amplifies a product in the mutant form of the correct allele. This can be used in conjunction with a wild-type specific assay to determine the genotype of the mouse. Homozygous mice will produce no amplification in the wild type assay shown below, which can also be used to confirm the targeting.

The mutant specific PCR on its own is not sufficient to confirm the targeting as the primer sites are within the homology arms of the construct. It can be used however to check that the mouse carries the mutation intended at the micro-injection.