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Analysis of EMS-induced temperature-sensitive sterility mutants of the Y chromosome of Drosophila melanogaster Ayles, George Burton


Heterochromatin can be described cytologically as those chromosomes or parts of chromosomes which remain heteropycnotic, or dark staining, through most of the cell cycle. Genetically and biochemically heterochromatic regions generally seem to be inert and it has been suggested that many heterochromatic loci are duplicated several times. In micro-organisms, genetic and biochemical analyses have been greatly facilitated by the use of conditional lethals which survive under "permissive" conditions but die under "restrictive" conditions. Temperature-sensitive ethyl methanesulfonate-induced lethal mutations (such mutants result in survival at 22°C but death at 29°C) have previously been used in Drosophila melanogaster for preliminary studies of development. In the present study 8 temperature-sensitive (ts) sterile mutations (males are fertile at 22°C but sterile at 29°C) were induced on the Y chromosome of D. melanogaster. The ts mutants were mapped genetically on the long arm of the Y chromosome and they were found to involve a minimum of 4 different loci. The Y chromosome of D. melanogaster is entirely heterochromatic and it is necessary for male fertility but the exact function of the Y chromosome is uncertain. The recovery of point mutations (ethyl methanesulfonate-induced temperature-sensitive mutations are presumed to be point mutations) on the Y chromosome indicates that there are loci on the Y represented by a single copy. A determination of the specific developmental effects of the ts sterile mutations, was also attempted. By exposing mutant males to a 48 hour period under the restrictive conditions (29°C) and observing their fertility for several days, the stage in the production of mature sperm during which the ts mutants were having an effect, was determined.

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