FINE-STRUCTURE MAPPING AND DELETION ANALYSIS OF THE MURINE PIEBALD LOCUS

piebald (s) is a recessive mutation that affects the development of tw o cell types of neural crest origin: the melanocytes, responsible for pigment synthesis in the skin, and enteric ganglia, which innervate th e lower bowel. As a result, mice carrying piebald mutations exhibit wh ite spotting in the coat and aganglionic megacolon. Previously the gen e had been localized to the distal half of mouse chromosome 14. To det ermine its precise location relative to molecular markers, an intersub specific backcross was generated. Two anchor loci of chromosome 14, sl aty and hypogonadal, in addition to simple sequence length repeat mark ers, were used to localize s to a 2-cM interval defined by the markers D14Mit38 and D14Mit42. The molecular markers were also used to charac terize nine induced s alleles. Three of these mutations exhibited no d eletions or rearrangements of the flanking markers, whereas the other six had two or more of these markers deleted. The extent of the deleti ons was found to be consistent with the severity of the homozygous phe notype. The location of deletion breakpoints in the induced alleles, c oupled with the recombination breakpoints in the backcross progeny, pr ovide useful molecular landmarks to define the location of the piebald gene.