Aresearcher is preparing to insert a human gene of interest into a bacterial plasmid in order to clone the human gene. she has genetically engineered the plasmid to carry a gene amp r , which confers resistance to the antibiotic ampicillin. she will include ampicillin in the plating medium when she grows the recombinant bacteria. why has she engineered the plasmid to include an antibiotic resistance gene?