A floxed neomycin resistance gene, as well as the 564 VkappaJkappa5 region from a hybridoma derived from an autoimmune SWRxNZB mouse, replaced a segment of DNA including the entire J kappa region. Male chimeric mice were bred to C57BL/6 females. Offspring from these mice were crossed with cre expressing transgenic mice in order to excise the neomycin resistance cassette. (J:113555)