si:\srii\ iiA oi DRosoi'iiii.A (;i:k.\i ci.i.i, .sia(;i:s ic; x irradi.vi ion 



melanogastvr, is most suited for such cxpn inicuts since not only can licritable 

 variations induced in it l)e easily detected and analysed I)ut technicjues have 

 been worked out for ensurinu; that one is treating and testing cells which 

 represent honioi^cneous samples (if distinct stages of mitosis or meiosis. 

 Since there are firm grounds for supposing that the same conditions as affect 

 somatic cells will affect those in meiosis and since the latter are ideal for the 

 analysis of induced heritable nuclear changes, the experiments to be re- 

 ported below have been carried out on the reproductive cells. While it was 

 recognized soon after Muller's demonstration of X-ray mutagenesis in 1927 

 that mature germ cells of both male and female fruit flies are much more 

 radio-sensitive than immature germ cells ^^ it took more than 20 years before 

 it was shown that there are various gradations of sensitivity amongst the 

 difTerent pre-meiotic and post-meiotic stages. This work, carried out 

 independently by several investigators and which will be referred to in con- 

 nection with our more recent work, was made possible by the elaboration of 

 more refined breeding technicjues which ensure the sampling of cells which 

 represent homogeneous groups at the time of treatment. 



PROCEDURE 



In the work which involved the treatment of male germ cells of Drosophila 

 melafwgasfer the following scheme was used. (Although this technique has 

 already been described'^, its applicability to work on mutation in general 

 and its ease of employment warrants our showing it again in order to 

 familiarize additional workers with its operation.) The treated chromosomes 

 are represented by asterisks: 



Pi y B 



SfC S|« •!! S(f ^ ^ ^ I^I J^ ^ ijC iji IjIJjCJjI !|CIjJ !^*}*S|«!]*S|C 



*************** ** ***** 



% sc«.Y(y+) 

 * 



^ o^ (treated) 



(non-yellow, Bar eyes) 



y sc^' In49 sc^ bw st pP^ 



X ? ? (virgin) 



y sc^' In49 sc^ bw st pP 

 (yellow, white eyes) 



y sc^' In49 sc^ bw st pP 



Fi 1 3 



*************** ** ***** 



% sc«.Y(y+) 

 * 



(non-yellow) 



y sc^' In49 sc^ bw st pP ^ 

 X 1 $ (virgin) 



y sc^' In49 sc* bw st pP 



(ycll(>\v, \vliitc eyes) 



F2 absence of independent assortment between bw and st, pP = autosomal 

 translocation. 



254 



