= Replica plating controls
<Replica plating controls> distinguish a growth <phenotype> from failure of the copying process. A replica on a <cell culture medium> that supports the starting <biological colonies> is a touch-transfer <scientific control>: growth at a site demonstrates that viable <biological cells> reached that control site. If a source is visible on the master but absent on both control and restrictive replicas, the restrictive readout is unresolved. If it grows on the control but fails on the restrictive replica, the difference is a candidate condition-dependent <phenotype>.
The touch-transfer <scientific control> still cannot guarantee transfer to every other replica. A known growing comparison on the restrictive <cell culture medium>, repeat sampling, and retesting a recovered source address different possible failures. Likewise, an orientation mark checks which source a site represents; it cannot check whether any <biological cells> arrived. Gentle, aligned contact helps preserve the map. In Investigations in Molecular Cell Biology by <Clare M. O’Connor>, section 12.6: Exercise 2 - Replica plating and complementation, the instructions align master and carrier marks and call for light, even contact.<Investigations in Molecular Cell Biology by Clare M. O’Connor/12.6: Exercise 2 - Replica plating and complementation>[Investigations in Molecular Cell Biology by Clare M. O’Connor; Introductory light-touch instruction and steps 1–2: orientation marks, aligned inversion and gentle even contact]{ref}
For <indirect selection of bacterial mutants>, keep the recovery route on the unexposed master. Returning a carrier that has touched a challenged replica to that master would introduce a possible exposure route. The original experiment's stray-<bacteriophage> check addresses contamination of the retained lineage, while the orientation and touch-transfer <scientific controls> address spatial identity and successful sampling. These questions must be checked separately.
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