512 KAISER AND JACOB 



-I H- 



, C02C|C0| mi 1% 



\ RECOMBINANTS 



1^ I I I 1 II I I I \-\^ 



47__30l5952cp, 



I n 



Fig. 1. A map representing recombination frequencies observed between pairs 

 of X mutants (Kaiser, 1957). The c segment is shown on an expanded scale. 



m5+, indicated that m^^ was present in 434 and that recombination can 

 occur between the m^ locus and the locus controlling immunity specificity. 

 Similar experiments were carried out with C02, Ci, coi, and mi. The markers 

 CO2, Ci, and coi cause the production of clear plaques, their corresponding 

 wild alleles controlling the production of turbid plaques. The marker 

 mi causes minute plaques with a halo. The results of these crosses, sum- 

 marized in Table 2, are that in the cross X X 434 recombination can occur 

 between ms, CO2, coi, and mi on the one hand, and the loci controlling the 

 specificity of immunity on the other hand. In crosses X X 21, recombina- 

 tion of ms, C02, and mi with immunity specificity can occur and in crosses 

 X X 82 the loci ms, coi, and mi can recombine with the loci controlling 

 the specificity of immunity. The pattern of recombination is similar in 

 the three types of crosses of X with 434, 82, and 21 in that recombination 

 can occur at the ends, m^ and mi, but not in the middle, Ci, of the X 

 linkage map. The three types of crosses differ, however, in the length 

 of the middle region which fails to recombine with the loci controlling 

 immunity specificity. In the cross X X 21 this region includes both C\ 

 and coi, in the cross X X 82 both coi and Ci, while in the cross X X 434 

 only cx fails to recombine. Because the region within which recombina- 

 tion fails to occur is the shortest for the cross X X 434, a more detailed 

 study of recombination between X and 434 was undertaken. Crosses 

 were made between 434 and a selected series of clear mutants of X. 

 The clear mutants were selected to mark different regions of the c 

 segment. 



The c segment of X consists of at least three regions. Each region is 

 probably responsible for the performance of a specific function in lyso- 

 genization (Kaiser, 1957). One mutant, number C44, was selected from 

 region III ; 4 mutants, C47, C30, Ci, and C50, from region I ; and two mutants. 



356 



