RECOMBINATION IN BACTERIOPHAGE 71 



yields of the two recombinants in individual bacteria is discernible in the cross 

 hXr7 and its reverse, but not in the other crosses. 



In the cross hXrU only two or three genetic exchanges occur during the 

 multiplication of the virus in a single bacterial cell. These exchanges take 

 place near the end of the period of multiplication of the virus. 



A hypothesis is outlined which is compatible with the genetic data and with 

 the results of Luria concerning reactivation of irradiated virus in bacteria 

 receiving two or more individually noninfective particles. The hypothesis is 

 an extension of that of Luria, according to which one visualizes genetic 

 interaction not between two viral particles, but between two sets of independ- 

 ently multiplying chromosome-like structures. Genetic exchange occurs either 

 by reassortment of these structures, or by something like crossing over between 

 homologous pairs, depending on the structural relation between the genetic 

 factors concerned. The interpretation made brings the linkage relations into 

 superficial agreement with the requirements of linear structure, but there is 

 little evidence that the genetic exchanges are reciprocal, and accordingly little 

 evidence that they are material exchanges. 



LITERATURE CITED 



Delbruck, M., 1945a Interference between bacterial viruses III. The mutual exclusion effect 



and the depressor effect. J. Bact. 50: 151-170. 



1945b The burst size distribution in the growth of bacterial viruses. J. Bact. 50: 131-135. 



1945c Effects of specific antisera on the growth of bacterial viruses. J. Bact. 50: 137-150. 

 Delbruck, M., and W. T. Bailey, Jr., 1946 Induced mutations in bacterial viruses. Cold Spring 



Harbor Symp. Quant. Biol. 11: 33-37. 

 Delbruck, M., and S. E. Luria, 1942 Interference between bacterial viruses I. Interference 



between two bacterial viruses acting upon the same host, and the mechanism of virus growth. 



Arch. Biochem. 1 : 111-141. 

 Dulbecco, R., 1949 The number of particles of bacteriophage T2 that can participate in intra- 

 cellular growth. Genetics 34: (In press). 

 Hershey, A. D., 1946a Mutation of bacteriophage with respect to type of plaque. Genetics 31 : 



620-640. 



1946b Spontaneous mutations in bacterial viruses. Cold Spring Harbor Symp. Quant. Biol. 



11:67-77. 

 Hershey, A. D., and R. Rotman, 1948 Linkage among genes controlling inhibition of lysis in 



a bacterial virus. Proc. nat. Acad. Sci. 34: 89-96. 

 Luria, S. E., 1947 Reactivation of irradiated bacteriophage by transfer of self-reproducing 



units. Proc. nat. Acad. Sci. 33: 253-264. 

 Luria, S. E., and R. Dulbecco, 1949 Genetic recombinations leading to production of active 



bacteriophage from ultraviolet inactivated bacteriophage particles. Genetics 34: (In press). 

 Rider, Paul R., 1939 An introduction to modern statistical methods, ix+220 pp. New York: 



Wiley & Sons. 



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