Linkage Analysis with Very High Frequency Males of Escherichia Coli.

ELL conjugation in Escherichia coli permits the oriented transfer of a specific linear array of genetic determinants from an Hfr, or male, donor cell to an F-, or female, recipient cell (WOLLMAN and JACOB 1955). The sequence of marker, transfer may vary from one Hfr type to another; moreover, any single Hfr type is capable of transferring only a fractional part of its entire genetic complement to recipient cells at high frequency. For example, six different Hfr types have been reported by JACOB and WOLLMAN (1957), each of which transfers a different chromosomal segment at high frequency. The discovery of this variety of Hfr types led JACOB and WOLLMAN to propose that the genetic markers of the original F+ strain which gave rise to the Hfr males are disposed on a closed circle (Figure 1 ) . The chromosome of any single Hfr type can then be described by breaking the circle at one point and designating as “origin” the free end which first penetrates the Fduring conjugation. The details of mating type determination and the role of the sex factor, F, in this process have been described elsewhere (WOLLMAN and JACOB 1958a; ADELBERG and BURNS 1960).