Kinetics of Phenotypic Expression 



203 



which have inherited the gene controlhng resistance, and in 

 which the character of resistance has become expressed, can 

 produce colonies. When the proportion of recombinant 

 colonies arising in the presence of the drugs becomes equal 

 to the proportion of control recombinants which have in- 

 herited and expressed the gene for resistance, expression is 

 regarded as complete. 



B. Segregation and expression 



180 240 300 20 40 60 80100120140160180 

 Time after dilution (min.) 

 Fig. 1 . The kinetics of segregation and phenotypic expression. 



To study the kinetics of segregation and expression in 

 nutrient broth, the zygote suspension is simply diluted 1 : 50 

 into fresh broth at the desired temperature. Samples are 

 removed as a function of time, appropriately diluted and 

 plated to synthetic minimal agar as well as to the same 

 medium containing a suitable concentration of the drug. 

 Results of two typical experiments are shown in Fig. 1. 



The continuous lines represent the kinetics of segregation, 

 and the interrupted lines the kinetics of phenotypic expres- 

 sion. With regard to segregation, it will be seen that on 

 synthetic minimal agar recombinants start to divide about 



