Positional cloning of the O7 gene. (A) Fine mapping of the O7 gene on chromosome 10. Names of the molecular markers, contig, BAC, and the recombinants are indicated (n = 13,933). ZMMBBb0166J07 and ZMMBBb0342E21 (abbreviated as b0166J07 and b0342E21) are the names of BAC clones covering this locus. The O7 locus was mapped to a ∼23-kb region containing gene1 and gene2 between the molecular markers LM4 and RM1. (B) Schematic representation of the gene structure of O7. The mutant sequence has a 12-nucleotide in-frame deletion in the second exon. ATG and TGA represent the start and stop codons, respectively.