抄録
On the grouping of gene mutations in Drosophila melanogaster, two cases are conceivable, namely, (1) grouping in one male, and (2) grouping in one chromosome. Although the present writers have met with examples for both of these cases, which were induced by neutron radiations from a cyclotron, the question whether or not the grouping is the characteristics of the neutron irradiation was not decided. The object of this experiment was to see whether X-rays also give rise to simultaneous occurrence of gene mutations in one male as well as in one chromosome. Unfortunately, an accident during the experiment prevented us from obtaining result from our study on (1), grouping in one male, so that only the case (2), grouping in one chromosome, can be dealt with here.
As to the procedure of the experiment, the ordinary “ClB” method for sex-linked lethals was used and the F2 maleless culture, which is regarded as the result of the presence of a lethal or lethals located in the treated X-chromosome, was carried to the next F3 generation. By inspecting the sex-ratio in the F3 offspring, it is possible to determine approximately whether the lethal mutation is either one in one chromosome or many in one chromosome, although by this method the detection is possible only when two or more lethals are situated so far apart from one another that a fairly large number of crossing over can take place between them.
In this way, out of 17 F2 maleless cultures induced by X-rays (rejecting the remaining 10 cultures with unreliable data) there was no case with two or more lethals per chromosome, whereas in our previous work in which neutrous were used, out of 18 F2 maleless culture tested there were 8 samples with two or more gene mutations in thee same X-chromosome.
Added in the proof. According to our second experiment recently repeated with X-rays 3000r in intensity, we found that “grouping in one male” could be also raised with X-rays. On the other hand however, “grouping in one chromosome” was also observed with extremely high rate (ca. 85 per cent). In view of the results described in this paper, it is difficult to understand such results and we are now going to repeat the experiment once again.
