Published online by Cambridge University Press: 14 April 2009
The genetical and developmental aspects of six dumpy mutants of Drosophila melanogaster have been investigated. The mutants obm, lm and olv (possibly alleles), lv, lv1 and lvI (possibly alleles) were known to be lethal when homozygous. Previously the lethal effect has been treated as a uniform effect. However, the lethal stage is not the same for all homozygotes, being egg/larval (E/L) for the three lv alleles, egg (E) for olv, larval/larval ecdysis (L/L) for lm and E/L and larval (L) for obm. Not all heterozygous combinations are lethal, i.e. obm/lm and obm/lvI are not lethal. Phenotypically the lethal heterozygotes fall into two patterns: (i) combinations not involving the allele obm and (ii) combinations involving obm. In the former, the mutant with the developmentally later expression is ‘dominant’ to the mutant with the developmentally earlier expression. In the latter, the genotypes manifest different proportions of individuals at the lethal stages E, E/L and L. Previous observations suggested that the lethality of the homozygote obm/obm was associated with the presence of an independent lethal in the stock. Observations presented here suggest that the lethality is a function of the obm allele itself. Complementation between some of the lethal mutants is not in accordance with the general rule for dumpy that compounds manifest the traits they have in common.