= D. Dressler
{c}
<D. Dressler> investigated the molecular mechanism of <genetic recombination>. With <H. Potter>, the researcher examined candidate <DNA> intermediates directly by <electron microscopy>, connecting a proposed strand-exchange mechanism to observable molecular forms.<On the mechanism of genetic recombination: electron microscopic observation of recombination intermediates by H. Potter and D. Dressler>[Byline and Abstract: microscopy of recombination intermediates]{ref}
The 1976 study isolated <Colicin E1 plasmid> <DNA> and cut it with the <restriction enzyme> <EcoRI>. Among the preparations were crossed structures containing approximately twice the normal plasmid DNA content. Their paired-length arms supplied a more specific structural test than the presence of an arbitrary crossing in a micrograph.<On the mechanism of genetic recombination: electron microscopic observation of recombination intermediates by H. Potter and D. Dressler>[Abstract and micrographs: EcoRI-linearized DNA and crossed forms]{ref}
The example illustrates why sample preparation can clarify a mechanistic question. Cutting circular molecules into lengths with known endpoints makes the organization of the candidate intermediate easier to compare with the prediction. Images provide structural evidence; the interpretation still requires appropriate preparation and biological controls.
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