这对引物pcrA320F(5’-GCGCCCACCACTACATGTAYGGNCC-3’)和pcrA598R (5‘-GGTGGTCGCCGTACCARTCRAA-3’)是我从英文文献Quantitative Detection of Perchlorate-Reducing Bacteria by Real-Time PCR Targeting the Perchlorate Reductase Gene。做实时定量PCR,我就不明白两对引物中为啥会有,Y,N,R这样非碱基的基团,大家说这是啥原因?