Expression pattern and chromosomal location of theOMP–lacZ transgene in H-lacZ6 mice. A, X-gal staining in the right heminose of a 3-week-old H-lacZ6 mouse is shown. The punctate pattern shown corresponds to the ORN subpopulation expressing the lacZ transgene (black dots). The majority of β-gal⁺ neurons is concentrated on endoturbinate-IIv(star); fewer neurons are scattered along the rostrocaudal axis of the OE (arrows).Endoturbinate-IId and -IIv, Dorsal and ventral aspects of endoturbinate-II. Scale bar, 1 mm. B, The transgene insertion site in H-lacZ6 mice (Hlz6 locus) maps to the proximal region of mouse chromosome 6, as determined by interspecific backcross analysis. Left, The segregation patterns ofHlz6 and the flanking genes (Ptn,Tcrb, and Hoxa5) were typed in 174 backcross animals. For individual pairs of loci, >174 animals were typed (see text). Each column represents the chromosome identified in the backcross progeny that was inherited from the C57BL/6J × M. spretus F1 parent. Theblack and white boxes refer to the presence of a C57BL/6J allele and an M. spretus allele, respectively. The number of offspring inheriting each type of chromosome is listed at the bottom of eachcolumn. Right, A partial chromosome 6 linkage map shows the location of Hlz6 in relation to its linked genes. Recombination distances between loci in centimorgans are shown to the left of the chromosome, and the positions of loci in human chromosomes, where known, are shown to theright. References for the human map positions of loci cited in this study can be obtained from the Genome Data Base, a computerized database of human linkage information maintained by The William H. Welch Medical Library of The Johns Hopkins University (Baltimore, MD).