The individual strands of these duplexes all are entirely heavy or entirely light. This pattern was confirmed experimentally in the mesolson-stahl experiment of 1958, which fallowed the semi conservative replication of DNA through three generations of growth of e.coli. when DNA was extracted from bacteria and its density measured by centrifugation, the DNA formed bands corresponding to its density-heavy for parental, hybrid for the first generation, and half hybrid and half light in the second generation.