X-Ray Induced Sex-Linked Recessive Lethals and Visibles in Sciara coprophila

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Abstract
A study was made of the sex-linked recessive lethal and visible mutations induced by X-rays in the sperm and ogcytes (first meiotic prophase) of S. coprophila. For sperm irradiated at 2000 r, 3000 r, and 4000 r the lethal rates obtained were 0.0136, 0.0303, and 0.0348 respectively. Sperm and oocytes irradiated at 4000 r gave approximately the same lethal rate, 0.0348 versus 0.0437. Two sex-linked recessives were recovered from the experiments on irradiated sperm (2/447 = 0.0044), an appreciable visible rate in view of the fact that only 5 sex-linked traits have been recovered heretofore in this species. On the basis of the experimental data the following interpretations have been made (1) Sciara is not resistant to the mutagenic effects of X-rays. The low yield of visible mutations obtained repeatedly in this genus can be attributed to a number of factors, including the unusual mode of inheritance and sex determination found in these flies. (2) There is no correlation between the induction of chromosomal aberrations and the induction of sex-linked recessive lethals. When the latter are used as a criterion of sensitivity to X-rays, the response of sperm and oocyte (first meiotic prophase) are not significantly different. When chromosomal aberrations are used as a measure of sensitivity, however, the sperm are found to be highly sensitive whereas the oocytes are completely insensitive (zero aberrations).