SPONTANEOUS MUTATION-RATES IN NULL AND BAND-MORPH MUTATIONS OF ENZYMELOCI IN DROSOPHILA-MELANOGASTER

Spontaneous mutations were accumulated for a total of 1,678,388 allele -generations in several hundred replicate second chromosome lines. The se lines were composed of a Cy chromosome and one of three different l ethal bearing chromosomes from natural populations. Electrophoretic mo bility and/or activity change was screened for seven enzyme loci. Fort y-four null mutations were detected, but no band-morph mutations were observed. There is significant variation in null mutation rate among e nzyme loci and among lethal chromosomes. This may be attributable to d ifferences in the distribution of transposable elements among the line s. The band-morph mutation rate is pooled with previous results and be comes 7.48 X 10(-7) with a 95% confidence limit of 2.04 X 10(-7) to 1. 91 X 10(-6) per locus per generation. Similarly, the pooled null mutat ion rate becomes 1.30 X 10(-5) with 95% confidence limit of 1.15 X 10( -5) to 1.52 X 10(-5) per locus per generation.