Annotation of combined sequencing reads of small RNAs extracted from 9 mouse serum samples. (A) Length distribution by abundance of the total reads mapped to the mouse genome (black bars), with reads annotated as mapping to either miRNAs (red bars), tRNAs (blue bars), rRNAs (green bars), or other small RNAs (yellow bars). Other small RNAs include scRNA, snRNA, and srpRNA. Note that the reads in the 20–24 nt and the 30–33 nt peaks are almost exclusively annotated as miRNAs and tRNAs, respectively. (B) A pie chart showing the percentage of reads mapping to the specific types of small RNAs. (C) Frequencies of 5′ tRNA half types represented in the aligned reads.