178 



H. MARCO VICH 



Then, the X-ray lesion of the Hfr expressed in the reconil)inants 

 must concern the transfer process, being either a damage to the trans- 

 mission of the genes from tlie Hfr to the recombinants or a letlial 

 mutation which might kill the zygote. The latter possibility may be 

 tested by interruption experiments. 



3. Effect of inferrupfion of conjugafiofi on survival of T+ L+ Sr re- 



comhinants 



In Fig. 3 are drawn the survival curves of the T+ L+ Sr recombinants 

 for several interruption times. No modification in the slope is observed. 



-O 



E 

 O 



E 



Duration of conjugation 



• 90 mm 



i 60mm 



O 30min 



« 1 min 



100 

 xlO-'rads 



Fig. 3. — The experimental conditions are the same as in Fig. 1. But the matings are 

 allowed to stand for a different length of time and then vigorously shaken and plated on 



selective synthetic agar. 



This eliminates the possibility that a dominant lethal, induced on the 

 chromosome, was transmitted to the zygote at the same time as the 

 T+ L+ markers. There remains, however, the alternative that such a 

 liy])othetical lethal mutation might exist only on the chromosome 

 segment between the TL loci and the origin "O" and, consequently, 

 will not apjjear with interruption experiment using these selected 

 markers. The following experiment will answer to this question. 



