Meselson and Stahl's experiments involved growing E.coli on a medium containing 15N (heavy nitrogen)which increased the density of the bacterial DNA.Cells were then grown on a medium containing only 14N.DNA samples were obtained for analysis after one,two and three rounds of replication (generations)and centrifuged on a density gradient.The double-helical DNA forms bands in the gradient depending on its density.How many bands did Meselson and Stahl see after two generation of cells were grown on the 14N medium?
A)One with DNA containing both 15N and 14N.
B)Two,one with DNA containing only 15N and one with DNA containing only 14N.
C)Two,one with DNA containing both 15N and 14N and one with DNA containing only 14N.
D)Three,one with DNA containing only 15N,one with DNA containing both 15N and 14N and one with DNA containing only 14N.

Question

Quizplus · Accepted Answer

After two generations of growth in 14N medium, Meselson and Stahl observed two bands: one with DNA containing both 15N and 14N (indicative of one round of replication in 14N, resulting in hybrid DNA) and one with DNA containing only 14N (indicative of DNA that had undergone two rounds of replication in 14N, resulting in lighter DNA). This supported the semi-conservative model of DNA replication.

Meselson and Stahl's Experiments Involved Growing E