Final answer:
In a conservative replication model, Meselson and Stahl would have observed two distinct bands after 1.0 generation: a heavy band for 15N parental DNA and a light band for 14N daughter DNA. After 2.0 generations, these bands would remain the same, with an increase in the light 14N band. This contrasts with their actual semi-conservative replication findings.
Step-by-step explanation:
If Meselson and Stahl had observed conservative replication, their experimental results would have differed significantly. After one generation in a conservative model, they would have observed two bands after centrifugation: one at the original 15N (heavy) position and one at the 14N (light) position, representative of the fully conserved parental DNA and the entirely new daughter DNA, respectively.
After two generations, they would have still seen the original heavy 15N band along with an increasing amount of the 14N light band, as more new DNA strands are synthesized. These hypothetical results contrast with the actual findings of Meselson and Stahl that supported the semi-conservative model of DNA replication, wherein DNA strands unwind and each parental strand serves as a template for the new strand, preserving the sequence information in each new DNA molecule.
Therefore, under conservative replication, after 1.0 generation, the distribution of DNA molecules would have consisted of one heavy band (full 15N) and one light band (full 14N). After 2.0 generations, there would have been one heavy band (15N) unchanged and an increasing light band (14N), with no intermediate bands present.