In Escherichia coli, the genes lac , gal , trp , and his are necessary for utilization of lactose, utilization of galactose, synthesis of tryptophan, and synthesis of histidine, respectively, and strs and strr are alleles for streptomycin sensitivity and resistance, respectively. You wish to carry out the cross HFR lac , gal , trp , his , strr X F- lac-, gal-, trp-, his-, strs What medium would you choose to select for gal and to select against strs in a mapping experiment

Minimal media + glucose + streptomycin

Explanation:

Those capable of synthesizing galactose can grow in minimal media, the availability of streptomycin will destroy those who are susceptible to the antibiotic, whereas glucose, a carbon source from which galactose may be produced and will encourage growth.

Therefore:

The medium should not include galactose when selecting for gal⁺.

Streptomycin should be present in the medium to select against .

The medium to choose is: Minimal media + glucose + streptomycin.