Discovery of recombination (sex) in E. coli -Lederburg and Tatum (1946)
Fertility factors, F+, F-, and Hfr strains
Hayes (1951) - the transfer is not reciprocal (i.e., it is directional).
Conversion of a recipient strain into a donor strain
Conversion occurs at a very high frequency
Discovery of Hfr strains
F+ episome (small circular DNA) has the genes for fertility (origins for replication), genes for the sexual machinery, e.g., pilus)
F+ episome can be transferred on its own (conversion)
F+ episome integrates at many places in the circular chromosome to give the various Hfr chromosome.
Integrated F+ episome DNA is transfer last in an Hfr strain.
Even Phage DNA can recombine - Benzer (1961) and T4 phage genetics
Mutations within a cistron can recombine
Fine structure mapping
Genes are not units of recombination
Using phage to map bacterial genes
Integration can be at one site (lambda) or many (mu)