Question

Imagine the Meselson and Stahl experiments had supported conservative replication instead of semi-conservative replication. What results would you predict to observe after two rounds of replication? Be specific regarding percent distributions of DNA incorporating 15N and 14N in the gradient.

a) 25% of DNA incorporating 15N and 75% incorporating 14N.
b) 50% of DNA incorporating 15N and 50% incorporating 14N.
c) 75% of DNA incorporating 15N and 25% incorporating 14N.
d) 100% of DNA incorporating 15N and 0% incorporating 14N.

Answer 1

In conservative replication, after two rounds, we would expect 75% of DNA to contain 14N and 25% to retain the original heavy 15N isotope.

Step-by-step explanation:

If the Meselson and Stahl experiments had supported conservative replication instead of semi-conservative replication, the expected results after two rounds of replication would have been different. In the conservative model, the original double-stranded DNA is conserved, and a completely new copy is made. Therefore, after one round of replication in 14N medium, we would see a 50% distribution of DNA with the original 15N isotope and 50% with the 14N isotope. However, after two rounds of replication, these results would shift to 75% of DNA incorporating 14N and only 25% retaining the original 15N label, as one-half of the original 15N DNA would have produced another 14N copy. Therefore, the correct answer would then be (c) 75% of DNA incorporating 15N and 25% incorporating 14N.