= 1973 plasmid construction experiment
In his account of the 1973 work, <Stanley Norman Cohen> describes purified R6-5 <plasmid> <DNA> cut with <EcoRI>, reassociated and joined by <DNA ligase>. The mixture entered <calcium chloride>-treated <Escherichia coli>; plates containing <antibiotics> selected <biological colonies> showing <antibiotic resistance>. The recovered pSC102 carried three R6-5 fragments and <kanamycin> <antibiotic resistance>. The team then joined material from pSC102 to the carrier pSC101 providing <tetracycline> <antibiotic resistance>, recovering pSC105 with both forms of <antibiotic resistance>.<DNA cloning: A personal view after 40 years by Stanley Norman Cohen>[Cohen (2013), The Hawaii Meeting and the Initial DNA Cloning Experiments, Figure 2 and Figure 3 caption; pSC102, pSC101 and pSC105 identities]{ref}
Stained <agarose gel electrophoresis>, gradient <centrifugation> and <electron microscope> comparisons characterized recovered <plasmids>. Parental and mixture lanes in Figure 3 supplied fragment comparisons; pSC101 alone gave one <EcoRI> fragment, while pSC105 combined its carrier fragment with the resistance-bearing fragment. This supported joined, propagating genetic material beyond selection alone. The comparisons did not determine every <nucleotide sequence> or establish a universal construction efficiency.<DNA cloning: A personal view after 40 years by Stanley Norman Cohen>[Cohen (2013), paragraphs describing the two laboratories' analyses and Figure 3, top and bottom: parental, mixed and recovered DNA comparisons]{ref}
The interesting inference combines two kinds of evidence: a recoverable <phenotype> identifies descendants worth examining, and the extracted <DNA> tests a structural explanation. The fragment comparisons are molecular <scientific controls>; they answer a different objection from a control for background growth. The hypothetical diagrams here illustrate that logic without reproducing the historical fragment lengths or <biological colony> counts.
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