Relation between mutation yield and cell lethality over a wide range of X-ray and fission neutron doses in maize

Episode von Medizin - Open Access LMU - Teil 02/22 von Ludwig-Maximilians-Universität München · 1. Januar 1974

Dry maize seeds, of a genetic stock heterozygous for the yellow-green locus (Yg^ Λ ^ ) ι were irradiated

with fission neutron doses up to 2700 rads and with 250 kVp X-rays to 40 000 rads. The frequency of

yellow-green (yg) sectors in seedling leaves 4 and 5 is largely a measure of the frequency of breakage (or

incomplete exchange) and loss of the part of the short arm of chromosome I X carrying Yj>. Plots of dose

versus yj* sector frequency per leaf show a linear increase with neutrons which reaches a maximum

(leaf 4 = S. 5, leaf 5 = 2. 5) followed by a rapid decline; and a curvilinear increase with X-rays reaching

a higher maximum (leaf 4 = 8. 5, leaf 5 = 3.6) followed by a decrease. The observed rise and subsequent

fall of numbers of yg_ mutations can be accounted for by a model in which the decline of the curves is

due to cell killing which may also be due to chromosome breakage and deletion. The interpretation is

based on the principles of the dual action theory, which explains radiobiological action in terms of microdosimetry.

One of the observations accounted for is the higher maximum mutation rate for X-rays as

compared to neutrons.

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