Diagrammatic representation of NBS profiling. Genomic DNA is cut with a single restriction enzyme that creates blunt-ended fragments. Asymmetric adapters containing short arms that are blocked with an amino group (denoted by A) to prevent extension by DNA polymerase are ligated to the ends of the fragments. Primers specific for NBS and the adapter long arm are used to amplify fragments containing the NBS sequence. Additional preceding asymmetric PCR is also often performed with the adapter primer and a limited amount of the NBS-specific primer, or alternatively only with the latter to increase the efficiency of NBS-specific amplification (see text for details). Black segment – NBS; pink arrow – NBS-specific primer; green arrow – primer specific for adapter long arm.