THE EFFECT OF X-RAYS ON THE FUNCTIONAL STRUCTURES OF THE Y CHROMOSOME IN SPERMATOCYTES OF DROSOPHILA HYDEI

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Abstract
At least 5 sites of the Y chromosome of Drosophila hydei form loops of specific morphology which seem to occur in correlation with a phase of activation of certain genes in spermatocyte nuclei. X-irradiation in doses of as low as 1,000 r causes characteristic morphological alterations of the loops. Exactly the same alterations have been observed earlier after treatment with actinomycin. The alterations are reversible. As expected and unlike actinomycin, X-irradiation causes also some irreversible damage; i.e., complete or partial suppression of loop regeneration, as well as breaks within the loops. The results are not inconsistent with the suggestion that in Drosophila spermatocytes the DNA-directed synthesis of RNA can be reversibly inhibited by X-irradiation.