3). !10 Points). A new mutant was isolated that is StrR and unable to use proline as a
carbon source (put). To determine where the mutation maps, it was mated
with the four different StrS put+ Hfr donor strains shown below.
[Arrowheads indicate the location and direction of transfer from each different Hfr.]
thrA (0 min.)
Hfr 3
Hfr 2
Hfr 1
Hfr 4
pyrC (23 min.)
cysA (50 min.)
cysG (73 min.)
metA (90 min.)
A). (2 Points). What is the selection for exconjugants in this experiment?
ANSWER: Growth on proline as a sole C-source.
B.) (2 Points). What is the counterselection against the donor cells in this
experiment?
ANSWER: Streptomycin resistance.
C). (6 Points). Given the results in the following table, where does the put
mutation
map? [Indicate the approximate map position in minutes.]
Donor Strain Put+ Colonies
Hfr1 200
Hfr2 500
Hfr3 70
Hfr4 10
ANSWER: About 40 min or near that region, in the region transferred early
between Hfr-2 and Hfr-1 but closer to the origin of Hfr 2.
