AP BIOLOGY

Detailed explanation-1: -Matthew Meselson and Franklin Stahl’s experiments on the replication of DNA, published in PNAS in 1958 ( 2), helped cement the concept of the double helix.

Detailed explanation-2: -The semiconservative mode of DNA replication was originally documented through the classic density labeling experiments of Matthew Meselson and Franklin W. Stahl, as communicated to PNAS by Max Delbrück in May 1958.

Detailed explanation-3: -The Meselson Stahl Experiment. A centrifuge was used to separate DNA molecules labeled with isotopes of different densities. This experiment revealed a pattern that supports the semiconservative model of DNA replication.

Detailed explanation-4: -Meselson & Stahl reasoned that these experiments showed that DNA replication was semi-conservative: the DNA strands separate and each makes a copy of itself, so that each daughter molecule comprises one “old” and one “new” strand.