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

Résumé

• 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.