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BENZER ET AL. 



Plaques of T2h, T2r, T2rh, andT2++ on B+B/2. 

 Tah: small, clear; Tar: large, turbid; Tarh: large, clear; T2 + + : small, 



turbid. 



bacterium. The relatively low yield of recombinants from such bacteria 

 does not seem unreasonable under such circumstances. 



5) The reciprocal cross, in which the infection is made with Tarh 

 and T2++, has also been studied. Here the single mutants Tar and 

 Tah appear as recombinants. Again, the two recombinants appear with 

 equal frequency and this frequency is the same as that with which the 

 recombinants Tarh and Ta + + appeared in the original cross. 



6) It will be shown below that there are several genetically distinct 

 r mutants of Ta. The principal ones studied by Hershey and Rotman 



