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A study of a dominant suppressor of the purple eye-color mutant in Drosophila melanogaster Firth, James Dawrant


The subject of this study is a new dominant suppressor mutation Su(pr) which acts on the purple eye-colour mutant (pr) of Drosophila a melanogaster. The Induction of Su (pr) was originally associated with the synthesis of a compound-2R chromosome In SD72/cn bw females. The suppression of p_ was first observed in combination with a homologous pr bearing compound-2L chromosome. Suppressed-pr flies appeared to have a fully wild eye phenotype. The intention of this study was to determine the chromosomal constitution necessary for Su(pr) induction, and to map the suppressor site. To do this, many compound-2R chromosomes were synthesized from several combinations of standard seconds. It was found that SD72 must be present to produce a suppressing compound-2R. The SD72 second carries a pericentric inversion that results in a duplication of 2L heterochromatIn, and an associated deficiency of 2R heterochromatin in the compound-2R S u (p r) chromosome. Suppression, therefore, Is associated with the pericentric inversion found only on SD72. The role of this segmental aneuploidy was studied by detaching several C(2L)pr: C(2R)SD72/,cn bw suppressed strains such that both arms of the Su(pr) compound autosome were recovered independently and established in standard strains. Suppressing and non-suppressing detachment products were recovered with a frequency that varied according to the compound-2R Su(pr) strain from which they were derived. The chromosome mechanics involved in the process of C(2R)SD72/cn bw formation and subsequent detachment implicates alterations to a segment of proxlmial 2R heterochromatin from SD72 in Su(pr) Induction. Loss of Su(pr) in the detachment process correlates predominantly with deletions generated In 2R heterochromatIn. Recombination mapping relative to the two visible heterochromatic markers, Iight and rolled, revealed that Su(pr) Iies to the left of rolIed. SpectrophotometrIc measurements of eye pigments revealed that suppressed-pr and suppressed-pru bw flies had pigment levels that exceeded the wild type. The lethal allele prc4. was not found to be suppressible.

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