Temperature-sensitive bobbed mutants in Drosophila melanogaster

Abstract

Temperature-sensitive mutants allelic to the NO region were isolated on the Y chromosome ofDrosophila melanogaster. Thebbts − 1 allele showed a minimal viability and extremebobbed phenotype at 18°C whereas at 29°C the viability and phenotype approached the wild-type condition. This allele is a typical cold-sensitive mutant. Thebbts − 2 allele had a maximum viability at both 18° and 29°C and a reduced viability at 25°C. The lethal phase of thebbts − 1 allele occurs during the late pupal stage. Thebbts − 1 allele showed no discrete temperature-sensitive period during the life cycle of the organism. This is compatible with the expectation that ats mutant in rRNA synthesis would not demonstrate a definite temperature-sensitive period since rRNA synthesis occurs during the entire life cycle. The number of rRNA genes for thets alleles was 117 forbbts − 1 and 127 forbbts − 2. These amounts represent deficiencies of rDNA of approximately 45 and 41%, respectively. This is the first report that partial deletions of a highly redundant locus can demonstrate a temperature-sensitive phenotype.