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A study of a possible new mutation, synpalpi, occurring in drosophila melanogaster Cole, Kathleen Margaret


The new mutation, synpalpi, which was found in the Xple Stock obtained from the Biological Supply House, Chicago, is so named because of the fusion of the antennae along the midline, all other Xple characteristics being normal except for a slight protrusion of the forehead. In stock cultures the mutant appears in greater numbers from normal Xple crosses than from synpalpi Xple crosses - with a predominance of female synpalpi. Experiments were carried out in order to determine the nature of the mutation, the type of inheritance involved, and the linkage group with which the mutation is associated. The mutant is not a gene mutation but a chromosomal aberration since Mendelian ratios were not observed to occur and since the mutation appeared irregularly but persistantly. A lethal factor is suggested by the small number of flies resulting from synpalpi crosses; the absence or small number of synpalpi in the F¹ of synpalpi crosses but its reappearance in 2-8% of the F² progeny; and by the death of flies in two different stages of development - early and late pupal stages. The association of the lethal factor with the "X" chromosome is assumed because few male synpalpi emerge. A deficiency of a part of the "X" chromosome would explain the death of the males and homozygous females. The possibility of a deficiency of a few bands at the tip of the “X” chromosome was substantiated by a review of the literature on deficient "X" chromosomes. It is believed that synpalpi flies are those deficient flies which do manage to survive and that the fused antennae are caused by the movements of the fly and forcing of fluid to the head in its efforts to extricate itself from the pupa case (its tracheae being attached posteriorly to the case). The Xple stock is very sensitive to variations from the optimum temperature of 25°C. Temperatures of 35°C., 29°C, and 15°C. increased the lethal effect of the deficiency - no synpalpi appearing in the F¹ or F² of temperature-treated cultures. In the test for linkage, the mutant appears to be associated with chromosomes I and III - therefore the mutant is not a simple deficiency of the "X" chromosome alone but appears to involve the third chromosome as well.

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