• The effect of x-ray dosage upon the frequency of induced structural changes in the chromosomes ofDrosophila melanogaster

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    • Abstract

       

      The frequency of induced structural changes of chromosomes observed inF1 female larvae ofDrosophila melanogaster raised from X-rayed males shows a direct linear proportionality with the X-ray dosage between 1000 and 4000 r.u. The relation of this fact to the “breakage” and “contact” hypotheses of their induction is discussed. Both hypotheses theoretically require sigmoid curves (with different characteristics) connecting dosage and effect. At intermediate doses the relation would be approximately linear on both hypotheses. The observations therefore do not provide any basis for discrimination.

      The high frequency (11%) of rearrangements, which on the contact hypothesis would require three or more threads in contact at one point, makes it unlikely that the chromosomes are ever in contact before, during or after irradiation unless they completely fill the treated nucleus.

      The high frequency of inversions in one chromosome arm, relative to interchanges between different arms, demonstrates a spatial preference either in the refusion of breakage ends or in a grouping of original breaks through a contact or analogous mechanism.

    • Author Affiliations

       

      D. G. Catcheside1

      1. the Rockefeller Foundation Wm. G. Kerckhoff Laboratories, California Institute of Technology, Pasadena
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  • Journal of Genetics | News

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