The genetics of a small chromosome region of Drosophila melanogaster containing the structural gene for alcohol dehydrogenase. IV: scutoid, an antimorphic mutation.

TLDR: The simplest hypothesis is that Sco is a small reciprocal transposition, the genes noc, osp, and Adh exchanging places with three genes normally mapping proximal to them: l(2)br34, 1( 2)br35 and rd.

Abstract: Exchange mapping locates the dominant mutation Scutoid to the right of Adh on chromosome arm 2L of D. melonogoster. However, deletion mapping indicates that Sco is to the left of Adh. The phenotype of Sco is sensitive to mutation, or deletion, of noc+ and of three genes, el, l(Z)br22, and l(2)br29 mapping immediately distal to noc. The four contiguous loci, el, 1(2)br22, l(2) br29 and noc, although separable by deletion end points, interact, because certain (or all) alleles of these four loci show partial failure of complementation, or even negative complementation. The simplest hypothesis is that Sco is a small reciprocal transposition, the genes noc, osp, and Adh exchanging places with three genes normally mapping proximal to them: 1(2)br34,1(2)br35 and rd. The Sco phenotype is thought to result from a position effect at the newly created noc/l(2)br28 junction. APPING close to the structural gene for alcohol dehydrogenase (Adh) on M chromosome arm 2L of Drosophila melanogaster is the dominant mutation Scutoid (Sco). This mutation was induced with X rays by KRIVSHENKO (1959) and, when heterozygous, results in a specific pattern of loss of bristles from the head and thorax of the adult fly. The map location of Sco made it an obvious marker to use for the genetic analysis of Adh and for the analysis of the genetic structure of the environs of Adh. It soon became apparent, however, that Sco is a rather exceptional mutation. For example, the map position of Sco determined by recombination and that determined by deletion analysis are contradictory. Moreover, Sco, although normally a stable mutation, can be reverted by X rays at a high frequency. Analysis of the revertants of Sco revealed an unexpected genetic complexity in the structure of the Sco chromosome. This and a following paper (M. ASHBURNER et al., unpublished results) are devoted to a genetic analysis of Sco and its revertants. It will probably help the reader if we begin by summarizing the structure of the Sco mutation that we consider the data warrant. MODEL