Fig. 2

Characteristics of retained introns. a Violin plots showing the log10 length distribution of non-retained (left violin in each subplot) and retained introns (right violin). Mann–Whitney U test was used to determine significance, denoted by *** (p < 0.001). b Generalized additive model with smoothness estimation of the intron length/IR ratio relationship. c Bivariate histograms illustrating strengths of splice site pairs (as maximum entropy) [37] of retained introns and all other introns using hexagon binning (100 × 100 bins). d Density of the GC content in retained (dark color) and non-retained introns (light color). Numbers indicate the mean GC content