= Lederberg replica plating experiment
{c}
<Joshua Lederberg> and <Esther Lederberg> reported <replica plating> in 1952. They <autoclave>-sterilized velveteen and secured it pile-up on a wood or cork cylinder with a metal hoop. Inverted <agar> plates touched the fabric lightly. Pencil marks or pin indentations fixed orientation. Complete-medium and minimal-medium replicas compared growth of <biological colonies>.<Replica plating and indirect selection of bacterial mutants by Joshua Lederberg and Esther Lederberg>[pp. 399–402, Methods: Replica plating; Figure 1 caption; Results: plate orientation]{ref}
<Escherichia coli> W-1 grew on plain <agar>; serial T-1 <bacteriophage> replicas showed resistant <biological colonies> at matching sites. Corresponding unexposed master regions seeded repeated broth-and-plain-<agar> enrichment, yielding resistant isolates. Stray-<bacteriophage> checks were negative; resistance persisted without challenge. This supported preexisting heritable resistance. The authors noted variable transfer and moisture-dependent resolution.<Replica plating and indirect selection of bacterial mutants by Joshua Lederberg and Esther Lederberg>[pp. 401–403: transfer variability, Clonal occurrence of phage resistant mutants, Indirect selection and stray-phage checks; p. 404, Discussion]{ref}
The <Luria-Delbrück experiment> uses variation between independently grown <cell cultures> to investigate the timing of resistant <mutations>. The <Lederberg replica plating experiment> adds a spatial route to a recoverable source: the tested samples identify an unexposed lineage. These are complementary arguments about <mutation> and <natural selection>. Growth readouts establish a tested <phenotype>; identifying the responsible <nucleotide sequence> requires other evidence, such as <DNA sequencing>.
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