Size distribution of unique smRNA signatures matching four different transposable element families. ( A) Gypsy. (B) Copia. (C) CACTA. (D) Mutator. The smRNA signatures with sizes above 24-nt were not included in this study since they were very few in comparison. The numbers on top of the bars represent the number of signatures for the most abundant size classes. The 22-nt signatures were the most abundant class for the Gypsy and CACTA families while the 24-nt were the most abundant for the Copia and Mutator families.