An ampicillin-resistant, tetracycline-resistant plasmid, is cleaved with the enzyme PstI, which cleaves within the ampicillin resistance gene. The cut plasmid is mixed with PstI digested Arabidopsis DNA and the mixture is used to transform antibiotic sensitive E. coli cells. The E. coli cells were plated on a medium containing ampicillin or tetracycline.
a) On which plate would you expect to see growth of bacteria containing plasmids with Arabidopsis DNA insert? Explain why?
b) Suppose you plated the E. coli cells, mentioned above, on a medium with both antibiotics, and a number of colonies were observed. How can you explain the presence of colonies that are resistant to both antibiotics.