Analysis of a Gene in Drosophila

Abstract

In the following the fine-structure analysis of the Notch locus in Drosophila and utilizing the recessive lethal N mutants, one gets a picture of the functional gene of cistron that does not differ materially from the picture of the gene of phage, Neurospora, and other microorganisms. The reason for this seems clear. The concept of the functional gene is a product of the genetics of microorganisms, and the methodology requires the use of mutants that in Drosophila are classified as amorphs. When the same mutant type is used in Drosophila, whether it be a recessive lethal like N or a recessive visible amorph like ry, the genes of macro- and microorganisms are similar. When hypomorphic mutants are used to the exclusion of the recessive lethal amorphs, the cistron cannot be clearly identified. It is suggested that the gene product of the Notch locus ultimately complexes with other products to form 2 or more different structural proteins or enzymes. Since 2 different mutant varieties of the same Notch protein (derived from 2 different hypomorphic mutants) need not affect the same enzyme system of the 2 or more systems to which the protein contributes, the trans heterozygotes may have a normal phenotype. Cytogenetic comparisons based upon Notch as a cistron and bithorax as an operan suggest that a single salivary band corresponds to a functional gene. However, it is the association of the genetic complexity at bithorax with multiple bands and the affinity of Notch with a single band that is of central importance, for, even if genetic interpretations change in time, the cytological difference must retain some meaning in its new context.