The majority of miRNAs expressed in SET2 cells are mixtures of different isomiRs. (A) Distribution of number of isomiRs per miRNA in the top 25% most expressed miRNAs and in the remaining more weakly expressed miRNAs. (B) Contribution of the major isomiR per miRNA to the total count, for classes of highly expressed miRNAs composed of 1 to 4 isomiRs.