General and specific effects of modifiers of mutant expression

Abstract
SUMMARY: Strains homozygous for mutants affecting the length of the L4 vein in Drosophila melanogaster were selected for increased or decreased vein length. Substitution of chromosomes selected for their effect on one mutant into the genome of a non-homologous mutant has shown that many modifiers of mutant expression must be considered as acting generally on the character rather than affecting only a specific mutant.