A) F- B) F+ C) F- D)Hfr E)Hfr/F F) F+ By accident, Hayes discovered a variant of his original donor strain that would not produce recombinants on crossing with the recipient strain. Apparently, the donor-type strains had lost the ability to transfer genetic material and had changed into recipient-type strains. In his analysis of this “sterile” donor variant, Hayes realized that the fertility (ability to donate) of E. coli could be lost and regained rather easily. Hayes suggested that donor ability is itself a hereditary state imposed by a fertility factor (F). Strains that carry F can donate, and are designated F+. Strains that lack F cannot donate and are recipients. These strains are designated F. An important breakthrough came when Luca Cavalli-Sforza discovered a derivative of an F+ strain. On crossing with F strains this new strain produced 1000 times as many recombinants for genetic markers as did a normal F+ strain. Cavalli-Sforza designated this derivative an Hfr strain to indicate a high frequency of recombination. In Hfr×Fcrosses, virtually none of the F parents were converted into F+ or into Hfr. This result is in contrast with F+×Fcrosses, where infectious transfer of F results in a large proportion of the F parents being converted into F+. portrays this concept. It became apparent that an Hfr strain results from the integration of the F factor into the chromosome Solution A) F- B) F+ C) F- D)Hfr E)Hfr/F F) F+ By accident, Hayes discovered a variant of his original donor strain that would not produce recombinants on crossing with the recipient strain. Apparently, the donor-type strains had lost the ability to transfer genetic material and had changed into recipient-type strains. In his analysis of this “sterile” donor variant, Hayes realized that the fertility (ability to donate) of E. coli could be lost and regained rather easily. Hayes suggested that donor ability is itself a hereditary state imposed by a fertility factor (F). Strains that carry F can donate, and are designated F+. Strains that lack F cannot donate and are recipients. These strains are designated F. An important breakthrough came when Luca Cavalli-Sforza discovered a derivative of an F+ strain. On crossing with F strains this new strain produced 1000 times as many recombinants for genetic markers as did a normal F+ strain. Cavalli-Sforza designated this derivative an Hfr strain to indicate a high frequency of recombination. In Hfr×Fcrosses, virtually none of the F parents were converted into F+ or into Hfr. This result is in contrast with F+×Fcrosses, where infectious transfer of F results in a large proportion of the F parents being converted into F+. portrays this concept. It became apparent that an Hfr strain results from the integration of the F factor into the chromosome.

1. A) F-
B) F+
C) F-
D)Hfr
E)Hfr/F
F) F+
By accident, Hayes discovered a variant of his original donor strain that would not produce
recombinants on crossing with the recipient strain. Apparently, the donor-type strains had lost
the ability to transfer genetic material and had changed into recipient-type strains. In his analysis
of this “sterile” donor variant, Hayes realized that the fertility (ability to donate) of E. coli could
be lost and regained rather easily. Hayes suggested that donor ability is itself a hereditary state
imposed by a fertility factor (F). Strains that carry F can donate, and are designated F+. Strains
that lack F cannot donate and are recipients. These strains are designated F.
An important breakthrough came when Luca Cavalli-Sforza discovered a derivative of an F+
strain. On crossing with F strains this new strain produced 1000 times as many recombinants for
genetic markers as did a normal F+ strain. Cavalli-Sforza designated this derivative an Hfr strain
to indicate a high frequency of recombination. In Hfr×Fcrosses, virtually none of the F parents
were converted into F+ or into Hfr. This result is in contrast with F+×Fcrosses, where infectious
transfer of F results in a large proportion of the F parents being converted into F+. portrays this
concept. It became apparent that an Hfr strain results from the integration of the F factor into the
chromosome
Solution
A) F-
B) F+
C) F-
D)Hfr
E)Hfr/F
F) F+
By accident, Hayes discovered a variant of his original donor strain that would not produce
recombinants on crossing with the recipient strain. Apparently, the donor-type strains had lost
the ability to transfer genetic material and had changed into recipient-type strains. In his analysis
of this “sterile” donor variant, Hayes realized that the fertility (ability to donate) of E. coli could
be lost and regained rather easily. Hayes suggested that donor ability is itself a hereditary state

2. imposed by a fertility factor (F). Strains that carry F can donate, and are designated F+. Strains
that lack F cannot donate and are recipients. These strains are designated F.
An important breakthrough came when Luca Cavalli-Sforza discovered a derivative of an F+
strain. On crossing with F strains this new strain produced 1000 times as many recombinants for
genetic markers as did a normal F+ strain. Cavalli-Sforza designated this derivative an Hfr strain
to indicate a high frequency of recombination. In Hfr×Fcrosses, virtually none of the F parents
were converted into F+ or into Hfr. This result is in contrast with F+×Fcrosses, where infectious
transfer of F results in a large proportion of the F parents being converted into F+. portrays this
concept. It became apparent that an Hfr strain results from the integration of the F factor into the
chromosome