THE EFFECTS OF X-RAY IRRADIATION ON SELECTION RESPONSE IN <i>ôDROSOPHILA MELANOGASTER</i>

Abstract

One of the most important problems in population genetics concerns how much genetic variation can be induced in the polygenic systems of various organisms by exposure to radiation, and the extent to which this variation affects the process of organic evolution. However, works dealing with spontaneous or induced mutations in polygenic systems in animals as well as in plants are rather few. Buzzati-Traverso (1953) reported in Drosophila that new variation induced by X-rays in polygenic systems can be utilized for natural selection under normal laboratory conditions. He has alsoshown that a rapid increase in fitness as measured by its main components, such as the number of eggs laid and the numbers of adult offspring, accompanies this increased mutation rate. Scossiroli (1953) reported a high efficacy of artificial selection for number of sternopleural bristles after irradiation in a strain that had previously reached a plateau under selection without irradiation. More recent works by several investigators on artificial selection for the number of bristles in Drosophila have shown more effective response under irradiation than under natural conditions Robertson, 1955, 1064;Scossiroli and Scossiroli, 1959;Tobari and Nei, 1965).The purpose of the present experiment is to clarify the mechanism by which new genetic variability available for artificial selection is induced by X-rays, and to estimate the amount of increase of polygenic variability in abdominal bristle numbers. The main result of this work has already published in Yamada and Kitagawa (1961). The details of the selection experiments after irradiation is presented in this paper. MATERIALS AND EXPERIMENTAL METHODSSelection was conducted for the total number of bristles on the fourth and fifth abdominal plates of D. melanogaster. Two strains were used as the base populations.The P strain was the isogenic Oregon-R strain. The C strain consisted of F2 flies from a cross between two isogenic strains, Oregon-R and Samarkand, each having been maintained by full-sib pair mating for several hundred generations.

Radiation-induced polygenic mutation in Arabidopsis thaliana I. Selection for flowering time

“…It seems unlikely therefore that induced mutation rates per locus are higher for polygenes than major genes (cf. Burdick and Mukai, 1958;Mukai, 1964), a conclusion also supported by the work of Kitagawa (1967). It must be admitted that maternal influences may have led to an overestimate of the doubling dose in the present experiments and it is possible that the seeds used had greater inherent radioresistance than those used by Robbelen and Veleminsky et al by virtue of different genotype or conditions of treatment.…”

P-element-induced mutation and quantitative variation inDrosophila melanogaster: lack of enhanced response to selection in lines derived from dysgenic crosses.

“…Second, it may help in finding out more about the nature of variation in quantitative traits, and their relationship to natural selection and evolution. Clayton & Robertson (1955), Kitagawa (1967) and Hollingdale & Barker (1971) showed that radiation increased mutation rate and hence response to selection in inbred lines of Drosophila. However it is considered (Enfield, 1986) that radiation is likely to produce a class of mutations skewed in the unfavourable direction, so radiation treatments are likely to provide only limited information about the contribution of naturally occurring mutations to response to selection.…”