Consider the function of the following genes in Escherichia coli. Lac^+ is requi
ID: 166750 • Letter: C
Question
Consider the function of the following genes in Escherichia coli. Lac^+ is required to utilize lactose as a carbon source. gal^+ is required to utilize galactose as a carbon source. trp^+ is required to synthesize the amino acid, tryptophan. his^+ is required to synthesize the amino acid, histidine. Str^R confers resistance to the antibiotic, streptomycin. You carry out the following cross. Hfr str^S lac^+ gal^+ trp^+ his^+ x F- str^R lac^- gal^- trp^- his^- In the Hfr strain, the str^s gene is known to be far from the origin of transfer. a. Which of the two strains is auxotrophic? Explain. b. What type of medium would you use to select F- recipient cells that are i. lac^+ ii. Gal^+ iii. trp^+ iv. His^+ v. gal^- and trp^+ vi. Lac^+ his^+ and trp^+Explanation / Answer
A. the F-strain is auxotropic it means it lacks some particular genes to synthesize amino acid and sugars.
B. Lac+ recepient cell will grow in selection media lacking lactose. Because it can synthesize lactose by itself.
Similarly, gal+ will grow on selection media lacking galactose, trp+ cells will need the selection media lacking trptophan, his+ cells will need the selection media lacking histidine.
To select the cells with gal+ and trp+ media lacking both galactose and trptophan is required whereas to select only lac+ , his+ and trp+ cells media lacking lactose, histidine and trptophan is required.