The interaction between two closely linked lethals in drosophila as the cause of the apparent constancy of the mutant „spread”

Abstract

1. By examination of the mutant „Spread” (wings) ofDrosophila melanogaster it appeared thatSpread, located in the IIIrd chromosome at 61, is not — asstated in the literature—recessive but dominant (to normal wings). 2. Spread acts lethally in double dose. 3. The wild type possesses a dominant indispensable factorVital (Vit) that is closely linked tospread. Its allelomorph,vit, also has a lethal effect in double dose. 4. The formula of the Spread mutant isSpr Vit/spr vit; thus it is double heterozygotic. It is only the strong linkage betweenSpr andVit that causes that the Spread type seems to be constant. 5. The distance betweenSpread andVital is scarcely 1.0. 6. The Spread mutant is an instance of a double heterozygote, which on account of the interaction of two lethal factors (Spr andvit) reminds of and has been construed as a constant homozygotic type.