X-RAY INDUCED MUTATIONS IN POLYGENIC SYSTEMS
Polygenic systems controlling quantitative characters have been shown to undergo spontaneous as well as xray-induced mutation. A number of polygenic systems controlling physiological and morphological traits were analyzed in a series of experiments. The increase in genetic variation induced by the treatments allowed a very marked shift in the mean value of several characters that were subjected to natural and artificial selection. In one set of experiments populations of Drosophimelanogaster in approximate numerical equilibrium were irradiated with 500, 1,000, 2,000, and 4,000 every two weeks, while control populations were kept in similar conditions but with no treatment. Both sets of populations originated from isogenic strains. After a number of generations it became evident that improvement in several traits affecting the fitness of the individuals was more rapid in the treated than in the nontreated populations. A genetic analysis of the traits affected showed that they were controlled by polygenic systems. In a second set of experiments strains that had been subjected to artificial selection for high and low number of sternopleural bristles for many generations and had reached a point where further selection was not giving any response, were x-rayed and further selected. While the mean number of bristles did not change appreciably in the control lines, in the treated lines it reached much higher levels in the plus-selection experiments, but remained unchanged in the minus-selection experiment. In both cases a marked increase in the genetic variability of the irradiated lines was demonstrated. In a third set of experiments an attempt was made to discriminate whether the observed increase in the genetic variability after x-ray treatment was due to mutations in polygenic systems or to the release of hidden variability, made possible through an increase in the rate of recombination produced by the effects of x rays. The results confirmed that the examined polygenic systems undergo spontaneous and x-ray-induced mutation. Applications of the findings in studies on problems of evolution and in plant and breeding programs are discussed briefly. (C.H.)
- Research Organization:
- Univ. of Pavia, Italy
- NSA Number:
- NSA-13-006195
- OSTI ID:
- 4266591
- Report Number(s):
- A/CONF.15/P/1391
- Resource Relation:
- Other Information: Orig. Receipt Date: 31-DEC-59
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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