Abstract
A recessive visible mutant, rbl was found in Kofu-Katsunuma natural populations of Drosophila melanogaster. It was frequently extracted from the same natural population and its equilibrium frequency in the population was assumed to be 0.04. The locus of rbl was determined to be 82.3 on the right arm of second chromosome and the mutant gene linked often with an heterotic inversion, In(2L)B, on the left arm. The homozygous flies for rbl had lower viability, developmental rate, productivity and fecundity than normal heterozygous flies. However, rbl heterozygous flies showed remarkable heterosis in productivity and fecundity though they were neutral in viability and developmental rate. In such a relation we may see the mechanism of persistent of rbl gene in natural populations. The role of inversion, In(2L)B, was assumed to enchance the heterosis of rbl gene or its closely linked genes at least in the cis-phase.
