This allele is derived from Cd79atm1Cgn by crossing mutant animals to a cre deleter line. Cre-mediated recombination results in removal of the floxed region containing endogenous exons 4-5. The deletion leaves behind duplicated exons carrying tyrosine to phenylalanine mutations at positions 182 and 193 of the ITAM motif. The correct sequence of the amino acid substitutions in mutant animals was verified by sequence analysis.