Practice question

Conservation of mass applies to restriction digestion: sum of fragment lengths equals parental molecule length when digestion is complete and no small fragments are lost in gel. Double digestion that generates 1.9 kb and 2.9 kb bands indicates parental construct of 4.8 kb because no other bands are detected and both fragments are accounted for. This additive relationship allows calculation of unknown plasmid sizes, verification of successful cloning, and detection of partial digestion or star activity. Accurate size estimation using DNA ladder on agarose gel makes it possible to reconstruct map and confirm recombinant integrity.