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Dominant temperature-sensitive lethal and semilethal mutations on chromosome 2 of Drosophila melanogaster. Procunier, James Douglas


Conditional lethal mutants which die under restrictive conditions but are viable in a permissive environment provide useful tools for the genetic and developmental analysis of certain loci. One class of conditional mutants, temperature-sensitive recessive lethals which die at 29°C but survive at 23°C has been reported for an extensive number of loci in Drosophila melanogaster. However, loci may exist which are highly redundant, or concerned with functions requiring the total output of both wild type alleles or with synthesis of a structural component which would pre-exempt their ready detection as recessive mutations. Mutations within such regions could, however, be recovered by selecting temperature-sensitive mutations which behave as dominant lethals at the restrictive temperature. In addition, such mutants would permit the first genetic characterizations of dominant lethals. Ethyl methanesulfonate-induced dominant temperature-sensitive lethal and semi lethal mutations were induced in chromosome 2. Twenty-one lethals of this type were isolated from 6,130 tested chromosomes and sixteen were characterized with respect to their genetic localization and developmental effects. Unexpectedly, eleven of the mutants were found to be closely linked to the dumpy, dp, locus. All eleven were recessive lethals at room temperature and were functionally allelic. The temperature-sensitive period (TSP) was similar for all cluster mutants although the effective lethal phase (LP) at 29°C differed. It was concluded that the cluster lethals are, in fact, genetically allelic. Three other loci were demonstrated by genetic recombination and each had a characteristic TSP and LP. In addition, two mutants caused sterility of females and could not be localized. The recovery of mutations which map genetically within a segment and are dominant lethals, proves that dominant lethality need not reflect gross chromosomal alterations in higher organisms.

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