You have identified a mutant E. coli strain that cannot synthesize histidine (His-).
To determine the location of the his- mutation on the E. coli chromosome, interrupted mating experiment was performed with 5 different Hfr strains. The following chart shows the time of entry (minutes, in parentheses) of the wild-type alleles of the first 5 markers (mutant genes) into the His- strain.
Hfr A ——– his (1) man (9) gal (28) lac (37) thr (45)
Hfr B ——– man(15) his (23) cys (38) ser (42) arg (49)
Hfr C ——– thr (3) lac (11) gal (20) man (39) his (47)
Hfr D ——– cys (3) his (18) man (26) gal (45) lac (54)
Hfr E ——– thr (6) rha (18) arg (36) ser (43) cys (47)
On the map below of the circular E. coli chromosome, indicate:
a. the relative location of each gene
b. the position where the sex factor is integrated in each of the five Hfr strains
c. the direction of chromosome transfer for each Hfr (indicate direction with an arrow).
