FREQUENCY OF SPONTANEOUS BACTERIOPHAGE MUTANTS 

 TABLE 1. BURST SIZE DISTRIBUTION, T2L ON B, SINGLE INFECTION 



Date 



Number 



of 



plates 



Average 



number 



of bursts 



per 



plate 



Average 

 yield 

 per 



burst 



Median 



Range" 



*The maximum values are almost certainly too high, since they probably represent plates 

 with two or more bursts. 



The Frequency Distribution of Mutants 



A total of 16 experiments, done between April 1949 and April 1951, yielded 

 the data to be reported. In five experiments, only the r mutants were scored. 

 The results are presented in Tables 2 and 3. A total of 90 plates with mutants r 

 and 103 plates with mutants w were observed. The expected number of plates 

 with both r and w mutants (calculated from the assumption of independent 

 incidence of r mutations and w mutations, either in the same bacterium or in 

 different bacteria whose bursts were pooled on one plate) was seven; six were 

 found. 



*Mutants w not scored. 



143 



