College

The labels for ten bacterial strains were mixed up, and now you do not know the identity of each strain. You know all strains are auxotrophs, and each one has a single, unique mutation. You set up pairwise crosses between bacterial strains and select for exconjugants by plating on MM (minimal medium).

Use the information below to determine F-, F+, and Hfr strains.

(- means no colonies grow on MM after conjugation, + means few colonies, +++ means many colonies)

Bacterial Strains Cross Results:
- B1B2B3B4B5
- A1 ++++++++-
- A2 ++++++++-
- A3 ----+
- A4 ----+
- A5 ----+++

Please explain why:

F- strains: A1, A2, B5
F+ strains: A3, A4, B3, B4
Hfr strains: B1, B2, A5

Determine the F-, F+, and Hfr strains:
F- strains: ______________
F+ strains: _________________
Hfr strains: _________________