In the classic Meselson and Stahl experiment, E. coli are first grown in 15N-enriched media (0th generation) and, subsequently, switched to 14N-enriched media. A DNA sample isolated during the first generation of E. coli grown in 14N media is subjected to a centrifugation step in a dense CsCl gradient. Assuming that replication occurs in a semiconservative fashion, the DNA sample will:
a) run as two bands (of equal intensity), one at the same position as a uniformly 15N-labeled DNA, and one at the same position as a uniformly 14N-labeled DNA.
b) run as one band, at the same position as a uniformly 15N-labeled DNA.
c) run as one band, at the same position as a uniformly 14N-labeled DNA.
d) run as one band, at a position expected for a DNA containing a 14N:15N ratio equal to 7.
e) run as one band, at a position expected for a DNA containing a 14N:15N ratio equal to 1.