The targeting cassette consisting of a SA.lox.PDGFRb.lox-Flpo-attB-Neo-attP cassette replaced the exons 2-4 of the endogenous Pdgfrb gene. The PDGFRb is a mouse Pdgfrb gene cDNA. PhiC31 integrase removed the attB-Neo-attP cassette. Cre-mediated recombination removed lox.PDGFRb.lox cassette from Pdgfrbtm1.1(flpo)Leol to enable the expression of the flpo recombinase. This is a nock-in-nock-out null allele. (J:306160)