In the Meselson-Stahl experiment, the mechanism for DNA replication was investigated using Escherichia coli [e-schuh-ri-KEE-uh koh-LY] as a model. E. coli was grown in medium with heavy nitrogen until all the DNA was labeled with the heavy isotope. Then, the E. coli was transferred to fresh medium with lighter nitrogen and the bacteria replicated once. The DNA was extracted from the bacteria using a density gradient to separate light-nitrogen DNA, heavy-nitrogen DNA, and light/heavy mixed DNA to decide whether replication was conservative or semiconservative. Which of the following results was predicted if replication was conservative?

W) All the DNA would be light

X) All of the DNA would be an intermediate density

Y) Half of the DNA would be light, and half would be heavy

Z) Half of the DNA would be intermediate, and half would be light
Y) HALF OF THE DNA WOULD BE LIGHT, AND HALF WOULD BE HEAVY