A segment on the chromosome of the T4 bacteriophage that was the first to be subjected to fine structure mapping. Mutants at the rII locus failed to produce plaques or produced abnormal plaques, depending on the strain of E. coli used as hosts. Benzer mapped over 1,600 of these mutations. In the diagram below, each is represented by a box and they reside in adjacent genes (cistrons A and B). The smallest unit of recombination (the recon) corresponded to a distance of two nucleotide pairs. The mutational sites (mutons) were the equivalent of one or two nucleotides. Note that each cistron contains a mutational hot spot. See Chronology, 1955, 1961, Benzer; 1978, Coulondre et al.; beads on a string, proflavin.
From S. Benzer, 1955, Fine structure of a genetic region in bacteriophage. Proc. Natl. Acad. Sci. 41: 344–354. Reproduced with permission of S. Benzer.
Subjects: Genetics and Genomics.