試題詳解

22. E. coli cells grown on 15N medium are transferred to 14N medium and allowed to grow for two more generations (two rounds of DNA replication). DNA extracted from these cells is centrifuged. What density distribution of DNA would you expect in this experiment?
(A) one high-density and one low-density band
(B) one intermediate-density band
(C) one intermediate-density and one low-density band
(D) one low-density band