316 C. LEVINTHAL 



interference is pair-wise and does not involve a third partner. However, 

 Edgar (1958) has also obtained results which indicate that the negative 

 interference occurs not when the heterozygous particles are being formed, 

 but when they produce further progeny. He finds that the number of observed 

 wild-type recombinants arising in a cross between very closely linked rll 

 markers increase by a large factor if the progeny of the cross is allowed to 

 grow for one cycle in B cells before being plated on K12 (A). The only apparent 

 source of this increase is the heterozygous particles in which the over-lap 

 spans both markers. This point can be definitively established, however, only 

 by single-burst experiments in which the progeny of individual heterozygotes 

 are examined. 



It is certainly not yet possible to estabHsh in any detailed sense a molecular 

 model of the recombination process in phage. Since, however, this is the 

 primary goal of much of the work on phage genetics, further studies will 

 probably combine chemical and physical studies with the more formal 

 aspects of genetic analysis. 



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