Chemistry and molecular measurement
Meselson studied at the University of Chicago and received his chemistry doctorate at Caltech in 1957. He developed equilibrium density-gradient centrifugation for analysing large molecules, allowing small density differences in materials such as DNA to be measured.
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DNA replication with Stahl
Meselson and Stahl applied this method to DNA replication, using isotope labels to distinguish old and newly synthesised material. Their 1958 experiments supported semiconservative replication in E. coli, with each daughter DNA molecule retaining one parental strand.
Recombination, messenger RNA and repair
With Jean Weigle he investigated DNA breakage and joining, and with Sydney Brenner and François Jacob he contributed to messenger-RNA research. After moving to Harvard in 1960, he and colleagues studied DNA restriction and mismatch-repair mechanisms.