5M 



JOSHUA LEDERBERG 



Table 5 



Segregation of Lac and Vi into prototrophs issuing from 

 various parental combinations* 



RECOMBINATIONS 



B-M-T+L+Bf B+M+T-L-Br B+M+T+L+ Lac~V{ Lac~V ',« Lac+V? Lac + \\ 



Lac + V, 



Lac Vi 



Bi + 602 303 



[45-8] [23.: 



Br*** 13 s 



[45] [28] 



Br** 244 157 



[42.8] [27.5] 



(D) (E) 



387 22 



[29-4] [1.7] 



8 o 



[28] [o] 



159 10 

 [27.9] [i.Q] 



(C) (triple) 



Lac+Vf 



Lac' V{ 



Bi + 107 145 9 61 



[33-2] [45-o] [ 2.8] [19.0] 



Br** 134 151 9 80 



[35.8] [40.4] [ 2.4] [21.4] 



(E) (D) (triple) (C) 



Lac-V? 



Lac+Vs 



Br 28 6 46 37 



[23-9] [ S-i] [39-3] [31-6] 



JBi - ** 102 7 201 91 



[25-4] [1.7] [5o.i] [22. 7I 



(C) (triple) (D) (E) 



* Cell mixtures of the indicated composition were plated into minimal agar plates or into 

 plates supplemented with thiamin. B± + types refer to scores of prototrophs picked at random from 

 minimal plates. 



** Br refers to colonies picked at random from thiamin supplemented plates. Although pre- 

 dominantly Br they contain B x + colonies in the proportion 1 : 10 as may be seen from table 4. 



*** Br- In this series, colonies were scored as to B\, and only the Bi~ are recorded. 



The letters (C), (D), (E), refer to crossover types corresponding to the regions [B M)-Lac; 

 Lac—V\\ and V t — [T L] respectively, according to the map of Fig. 2d. 



t Test for allelism. 



On the basis of table 5, the factors V\ and Lac may be brought into the argu- 

 ment. In addition to the joint segregations of these factors, the effect of the B\ 

 segregation was studied in the following way. It would be uneconomical, in 

 view of the relative paucity of Bi + types, to separate these from the Br~ by 

 nutritional testing of colonies which appear on thiamin supplemented agar. 

 Instead, the entire sample was regarded as Br~ with the proviso that it might 

 be contaminated to the extent of ten percent with Bi + . However, it has been 

 found that the distribution of Lac and V on colonies picked from thiamin 



152 



