A study of dominant mosaic eye-color mutants in Drosophila melanogaster

1. Six dominant mosaic eye-color mutants of the brown locus (II - 104.3) have been studied. All are over lethal when homozygous. The homozygotes are characterized by non-mosaic eye-color, and by wing abnormalities. These allelomorphs affect principally the yellow pigment of the eye, reducing or removing it entirely. 2. Four of these six are associated with mutual translocations; two with inversions only. In each case one of the breaks is at or very close to the locus concerned. 3. Flies have been obtained retaining the mutual translocation, but with normal eye-color. 4. One dominant allelomorph (Grape) of the mutant pink (III - 48.0) has been studied. It too affects the amount of the yellow pigment present in the eye. It is associated with a mutual translocation, and one break is at or very near the locus concerned. 5. Two dominant allelomorphic mosaic eye-colors (Moiré) located in the left arm of III are associated, one with an inversion, the other with a mutual translocation. 6. More than half of all chromosomal breaks occur in the immediate vicinity (genetic) of the spindle-fiber attachments in II and III. 7. When a break occurs in a subterminal region, crossing-over is affected in that arm in an amount which varies with the distance from the break. 7. When a break occurs near the spindle-fiber, crossing-over is very little affected in either arm. 8. Dobzhansky and Sturtevant's finding that crossing-over in a mutual translocation is increased in one chromosome when it is simultaneously inhibited in the other, is confirmed. 9. The ratio of orthoploid to aneuploid gametes in the cases studied is 1.4 (or 1.5) : 1. The existence of extremely aneuploid gametes is uncertain. 10. It is shown that in certain cases two chromosomes must have undergone synapsis in the form of a ring. This shows that crossing-over need not begin near the spindle-fiber and progress outwards, as has been suggested (Bridges and Morgan, '23; Graubard, '32). 11. A method is described for accurately determining the location of the spindle-fiber attachment with reference to known neighboring genes by means of the segregation of gametes in a mutual translocation. 12. A means is described for testing Serebrowsky and Dubinin's hypothesis that translocations and inversions occur by exchanges at points of contact between intertwisting chromosomes or portions of chromosomesEcology, Evolution and Behavio