The induction of chromosome losses inDrosophila sperm and their linear dependence on dosages of irradiation
1. A method for detecting non-lethal losses ofX- andY-chromosomes produced by irradiation of mature sperm ofDrosophila is described in detail.
2. Losses ofX andY are found to be produced by X-raying mature sperm, and those found by the method used are non-lethal to the zygote.
3. Between 0 and 4000 r. the frequency of the above losses is, in first approximation, a linear function of the dosage, and it certainly varies less rapidly than the 1·5 power of the latter—the power found, for these dosages, in the case of gross rearrangements.
4. The mechanism of origination of these losses is interpreted as being through the occurrence of single breaks followed by lateral fusion of sister chromatid fragments, leading to formation of a dicentric chromosome which is either lost in the first change or becomes subjected to repeated breakage at successive anaphases and is ultimately lost.
5. It is suggested, as a result of comparisons of the frequency of the losses found with the amount of change of the sex ratio caused by the same dosage, that a major part of the losses are lethal to the zygote.
Volume 100, 2021
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