La Mosca Linda

THE MINIATURE COMPLEX I N DROSOPHILA
MELANOGASTER
HERMAN M. SLATIS AND DAVID A. WILLERMET Department of Genetics, McGill University, Montreal, Canada Received April 30, 1953

A 1-36.1

CCORDING to BRIDGES BREHME and (1944), the miniature locus (m, ) was discovered in August, 1910, and the gene has frequently recurred spontaneously and as an induced mutant. Immediately adjacent to m is thesimilar mutant dusky ( d y ) , which has been placed at 36.2, although not on the basis of crossover data (STURTEVANT TAN1937). Almost no and work has been done on these mutants in Drosophila melanogaster, and little light has been shed on the relations between them by comparative studies of other species in the genus. STURTEVANTTAN and (1937) also found no crossovers in D.pseudoobscuru. Reportsfor D.virilis ( CHINO1936), D . ananussue (KIKKAWA 1938), and D . hydei (SPENCER 1949) show some crossover distance between the two sex-linked loci which are assumed to correspond to m and dy in these species, but in each case the relative positions have not been tested directly, but have been calculated by mapping with a third locus. Further testing of D . virilis (KOMAI and TAKAKU 1949) hasresulted in the finding of 8 wild-type flies among 22,334, a number too large to be ascribed to back-mutation (apparently markers were not used to identify crossovers). It may be assumed that an equal number of m d y flies occurred but were not recognized, giving a crossover value of about .07%. The small size of both m and d y wings is produced in an embryologically similar manner by decreasing thesize of the cells (DORZHANSKY WADD1929; INGTON 1940). Both also cause a darkening of the wings, and there is a distinct change in the character of the wing epithelium such that moderately large winged flies like dusky may most readily be distinguished from wild type by their failure to reflect light in the same way that the wild type does. As this paper will show that there is a relationship betweenm and dy, these loci will be referred to as the “ miniature complex.’’
MATERIALS AND METHODS

The miniature complex alleles used in this study were m, m2259-4, and mD, dy. The m and dy alleles are of unknown origin, but may be presumed to be the standard mutants known by these designations, and therefore are of spontaneous origin. The m259-4 is an X-ray induced deficiency discovered by alleleDEMEREC. has been stated to be deficient for m but not d y . The nzD allele It was provisionally reported by SLATIS1949). The following description of ( this allele may be considered to be definitive.
GENETICS39: 45 January
1954.

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HERMAN M. SLATIS A N D DAVID A. WILLERMET

mD: miniature-dominant SLATIS, 481317. From X-ray treatment of bw; st male, as one female with a small right wingbut a wild-type left wing. No subsequent individuals have shown this mosaicism. Homozygotes about same size as homozygous nz d y and 5/6 as large as homozygous m wing. mD/+ almost precisely between mD/vnDand +/+. Viability about 20% to 50% in hemizygotes and 5% in homozygotes. Death occurs largely in the egg. Very low fertility in homozygous females. No evidence of a chromosomal aberration fromcrossover data or salivary gland analysis. Apparently allelic to m and dy. RK3.

Miniature-dominant may be carried in stocks balanced by CLB without any selection. It should prove a useful marker of the center of the X chromosome. The relative effect of different genotypes was measured by comparing flies from the same bottle whenever possible, since this eliminates the variables which occurbetween cultures. Except for cytological studies, flies were raised in half-pint bottles at 25°C. The mutants vermilion ( v , 1-33.0) and garnet (9, 1-44.4) and the CLB chromosome were used as markers. Evidence will be presented to support the assumption that these markers have no effect on wing size. In part of these experiments the wing length was measured from the base of the subcostal vein...