Recombinant dna molecules contain dna from two different sources. Recombinant-dna techonology can change the genetic composition of living organisms. /plasmids are circular dna molecules found in bacteria and yeasts, they are widely use by scientists studying recombinant dna, because dna joined to a plasmid can be replicated. /a genetic marker is a gene that is used to differentiate a cell that carries a reconbinant plasmid from those that do not.