THE CYTOGENETICS OF A RECESSIVE VISIBLE MUTANT ASSOCIATED WITH A DEFICIENCY ADJACENT TO THE NOTCH LOCUS IN DROSOPHILA MELANOGASTER

D. O. Keppy ¹ and W. J. Welshons ¹

¹ Department of Genetics, Iowa State University, Ames, Iowa 50011

The recessive visible fa^swb allele in Drosophila is an interband deletion between salivary band 3C5, 6 and 7. Heterozygosity for the deletion does not suppress recombination between fa^swb and mutant sites at Notch adjacent to it.—Df(1)w^67k30, deficient for salivary bands 3C2 to 6, is to the left of fa^swb. By crossing over within the homologous bit of interband retained in w ^67k30 and fa^swb, the two deficiencies can be linked. Cytologically, 3C7, "fused" to 3C5, 6 in fa^swb, becomes "fused" to 3C1 when the two are coupled. In the double deletion, the recessive visible phenotype of the fa^swb "allele" is suppressed. Both w^67k30 and fa^swb can be recovered by uncoupling the two deficiencies.—The data suggest that the mutant fa^swb does not represent a lesion at Notch; the entire gene or locus seems to be present. The interband deletion in fa^swb has secondarily moved an intact Notch locus to a foreign environment that interferes with its normal function. When fa^swb is linked to w^67k30, the interference is eliminated and normal Notch functions resume.—The position of Notch on the salivary gland chromosome is reviewed in relation to the information obtained in these experiments.

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