Page "Bacterial conjugation" Paragraph 8

A cell culture that contains in its population cells with non-integrated F-plasmids usually also contains a few cells that have accidentally integrated their plasmids.

It is these cells that are responsible for the low-frequency chromosomal gene transfers that occur in such cultures.

Some strains of bacteria with an integrated F-plasmid can be isolated and grown in pure culture.

Because such strains transfer chromosomal genes very efficiently they are called Hfr ( high frequency of recombination ).

The E. coli genome was originally mapped by interrupted mating experiments in which various Hfr cells in the process of conjugation were sheared from recipients after less than 100 minutes ( initially using a Waring blender ).

The genes that were transferred were then investigated.