Developmental genetics of thoracic abnormalities of dumpy mutants of Drosophila melanogaster.

HE mutant alleles of the dumpy locus produce a number of phenotypic Teffects, viz., an obliquity of the wings ( 0 ) , a lethal effect (1) , and hypodermal irregularities of the thorax called vortices (v) . The genetics of the dumpy locus has been described by CARLSON (1959). The alleles may express any one of the three effects singly (dp", d p z , dp") or in any combination with one another (dpoz , dpzv , dp"", d p o z v ) . There is also a comma mutant ( c m ) characterized by commalike invaginations at the anterior thorax. There is some intragenic complementation among the alleles in the trans configuration, for example, ou/Z is wild' type. Heterozygous combinations manifest the trait common to both alleles, for example, ou/u manifests thoracic abnormalities. This paper is about allelic combinations which produce thoracic abnormalities. A total of five thoracic abnormalities have been described. The existence of three of these, viz., first vortex (v), second vortex (2nd v) and comma (cm) has been known for some time. They are expressed on the scutum and each abnormality when manifested causes some local disturbance in the bristle pattern. The other two abnormalities, pre-episternal pit and posterior invagination, have only recently been described (METCALFE 1969). The presence of these abnormalities, owing to their positions on the thorax, is not associated with disturbances in the pattern of microchaetae. All five thoracic abnormalities have various forms; namely, pits, eruptions, or raised pits (an expression intermediate between the former two) of the cuticle. This paper reports the phenotypic patterns of abnormalities produced by the different v-producing alleles; the developmental history of the thoracic abnormalities which determine the variations in form of the abnormalities; and the morphogenetic distinctiveness of each v-producing allele. The results are presented in four sections: SECTION I describes the phenotypic patterns of abnormalities manifested by the v-producing allelic combinations. SECTION 11 reports the development of the thoracic abnormalities (invaginations of the hypodermis) ; their similarities and differences; and associated muscle breakdown in a dp"" stock-this genotype being chosen because it manifests four of the five abnormalities and is not lethal when homozygous. SECTION 111 deals with the internal as opposed to the external phenotype of adults of v-producing allelic combinations, i.e., differences in the size of invaginations and the amount