Benzer developed "the T4 rII system, a new genetic technique involving recombination in T4 bacteriophage rII mutants. After observing that a particular rII mutant, a mutation that caused the bacteriophage to eliminate bacteria more rapidly than usual, was not exhibiting the expected phenotype, it occurred to Benzer that this strain might have come from a cross between two different rII mutants (each having part of the rII gene intact) wherein a recombination event resulted in a normal rII sequence. Benzer realized that by generating many r mutants and recording the recombination frequency between different r strains, one could create a detailed map of the gene, much as Alfred Sturtevant had done for chromosomes.^[8] Taking advantage of the enormous number of recombinants that could be analyzed in the rII mutant system, Benzer was eventually able to map over 2400 rII mutations. The data he collected provided the first evidence that the gene is not an indivisible entity, as previously believed, and that genes were linear" (Wikipedia article on Seymour Benzer, accessed 7-22).

Digital facsimile of the 1959 paper from PubMedCentral at this link. See also Benzer's "On the topography of the genetic fine structure," Proc. Nat. Acad. Sci., 47 (1961) 403-415. Digital facsimile of the 1961 paper from PubMedCentral at this link.