Fused (Fu) is a dominant mutation in mice resulting in the asymmetry and fusion of tail vertebrae in heterozygotes. Fu/Fu homozygotes are often viable and can exhibit a duplication of the terminal tail vertebrae resulting in bifurcated tails. There are two more severe alleles at Fu, Kinky (Fu(Ki)) and Knobbly (Fu(Kb)), which die between 9 and 10 days of gestation as homozygotes, exhibiting a duplication of the embryonic axis, leading to incomplete or complete twinning. To define the precise map position of the Fu(Ki) mutation on mouse Chromosome 17, a 983-animal (Fu(Ki) tf x Mus spretus)F1 x + tf/+ tf interspecific backcross was generated and scored for Fu(Ki), another tightly linked visible marker tufted (tf), and five linked molecular loci, D17MIT18, D17Leh54, D17Aus57, Hba-ps4, and Pim1. The order and genetic distances between the markers were determined to be centromere- D17MIT18-5.79 cM-D17Leh54-0.85 cM-D17Pri6-0.12 cM-D17Pri7-0.12 cM-Hba-ps4- 1.20 cM-D17Pri8-0.48 cM-tf-2.05 cM-Pim1. The Fu(Ki) gene could not be genetically separated from three molecular markers, D17Pri6, D17Pri7, and Hba-ps4. Yeast artificial chromosome clones that contain these tightly linked markers have been isolated to form a contig that contains Fu(Ki). Recombination breakpoints generated through the interspecies backcross were mapped onto the contig and demonstrate that recombination in this region is not random.
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