Fig. 1

Expression of piRNA and mRNA of P elements in adult ovaries of F1 progenies in cross A*. a Small RNA reads (23–35 nt in length) mapped to the sense (green) and antisense (red) strands of the P element are shown on the P-element structure (bottom). Har (top) was a P strain and used as a control. b Frequencies of length (0–25 bp, x-axis) of overlapping regions between sense and antisense small RNAs (23–35 nt) identified in ovaries of F1 progenies. An overlap of 10 bp is a signature of piRNA pairs produced via the ping-pong cycle. c The expression levels of ping-pong-paired piRNAs in F1 ovaries normalized by miRNA (reads per million [RPM] miRNAmiRNA reads). The strain names of mothers are shown in black (P), red (M′), and blue (Q). d The relationship between the log expression levels of mRNAs (y-axis) and ping-pong-paired piRNAs (x-axis) of P elements in F1 ovaries. The strain names of mothers are shown in black (P), red (M′), and blue (Q). The Pearson’s correlation efficient is shown on the top. e A tree of hierarchical clustering of the nine natural strains and the Har strain based on the data shown in panel c. The strain names of mothers are shown in black (P), red (M′), and blue (Q). The M′ strains are clustered together