A single mutational event was used to target two genes, Bglap1 and Bglap2. A construct containing the neomycin resistance gene deleted exon 4 of Bglap1 and the entire coding region of Bglap2 by homologous recombination. A third locus in this cluster, Bglap-rs1, was left intact. Expression analysis of total RNA isolated from homozygous mutant bone showed an absence of normal transcript, while Western blot analysis revealed a lack of protein. A radioimmuno assay further confirmed the abrogation of the two loci. (J:34440)