Heat Induced Mutations in Drosophila

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Abstract
In 10 experiments involving different stocks and matings, 6-day-old larvae of D. melanogaster were exposed to 36[degree] C. for 24 hrs. Offspring of these heated flies and controls from the same parents were examined and all variations tested for at least 5 generations following the heat. In all, nearly 200,000 offspring of heated individuals and 100,000 controls were observed. In the first 5 generations after exposure, 44 mutations occurred in experimental lines and 3 in control lines, an increase of nearly 6 times following heating. The frequency of X-lethals and autosomal re-cessives was 150 times that of dominant mutations when the number of flies tested for each is considered. Mutations occurred in 24 loci, 10 of which mutated twice and 2 mutations 4 times each, suggesting a specific reaction to the treatment. Further heating of these new mutations from heated lines did not cause further allelo-morphic mutations in the same loci. Mutations occurred in treated [male] and [female] lines at equal rates. At least 1/3 of the mutations were of such a nature that they must have occurred later than the time of exposure, suggesting a delayed effect of the heat on the genes. Non-inherited somatic variations showed a significant increase in heated lines, but among offspring of [female][female] only, indicating an inherited cytoplasmic change caused by the treatment. The data suggest that temp. changes may hasten the evolutionary process by increasing the mutation rate.

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