Aplasmid that encodes resistance to ampicillin and tetracycline is digested with the restriction enzyme psti, which cuts the plasmid at a single site in the ampicillin-resistance gene. the dna is then annealed with a psti digest of human dna, ligated, and used to transform e. coli cells. (a) what antibiotic would you put in an agar plate to ensure that the cells of a bacterial colony contain the plasmid? (b) what antibiotic-resistance phenotypes will be found on the plate? (c) which phenotype will indicate the presence of plasmids that contain human dna fragments? why does lowering the ionic strength of a solution of double-stranded dna permit the dna to denature more readily (for example, to denature at a lower temperature than at a higher ionic strength)?