The Cytogenetic Analysis of a Fractured

The data presented in this study are derived from the analyses of Notch mutants known to be associated with visible cytological deficiencies. One mutant, Df(l)Nfirb1, described as a right-side deficiency, bears a deletion that apparently initiates within the Notch locus and extends to the right as far as the locus of dm. Recombination experiments using heterozygotes of Df(1) Nfiebl with a series of intragenic point mutants within the Notch cistron suggest that this deficiency represents a deletion for the right-end portion of the gene. A consideration of the cytology of Df(1)N62bf supports the cytogenetic inference that, if a Notch locus-3C7 relationship is valid, the missing portion of the gene as assayed by recombination experiments has an interband position between 3C7 and 8.-The data derived fmm two left-side deficiencies with a genetic lesion in Notch and a deletion extending to w are somewhat equivocal, but they do support the presumed Notch locus-3C7 band relationship and thereby enhance the likelihood that Df ( I ) N62b1 is cor1 ectly interpreted.-Cytogenetic information presently available suggests that, although a significant portion of the Notch cistron has a position on the salivary map identified as interband 3C7 to 8, the 3C7 band is part of the total picture of the Notch gene. FOR many years the sex-linked Notch locus has been an object of study, and a great amount of relevant information is already available. A typical Notch mutant ( N ) behaves as a recessive lethal in the homozygous or hemizygous condition. In heterozygotes of the genotype N / + , the mutant acts like a dominant; females display an abnormal phenotype consisting of notched wings, often associated with thickened wing veins, and subtle changes occur in the distribution of thoracic microchaetae. The fact that N mutants could be detected in a single dose undoubtedly contributed to the selection of the locus for investigation, and, subsequently, cytogenetic information appeared in the literature. MOHR (1919, 1923) reported on the genetics and cytology of an N mutant associated with a visible deficiency for a considerable portion of the salivary X chromosome. Later, DEMEREC (1939) induced a great number of N mutants which were analyzed cytologically and were found to be either free of aberrations or associated with deficiencies. inversions and translocations. Continued analysis of deficiencies led to the conclusion that the loss of salivary band 3C7 was the cause of the mutation to N (SLIZYNSKA 1938; DEMEREC 1939). When stable muJournal Paper No. 5-7651 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, Project 1985. Work supported in part by National Science Foundation grants GB-8651 and GB307M Work performed in No part w h l e on a Faculty Improvement Leave granted by Iowa State Uruversty Genetics 76: 775-794 April 1974