Regionality versus. precision of nucleosomal variation. a Analysis of BY/RM SNEPs. For each histone mark, regionality of variation was examined by counting, for each SNEP, the frequency of SNEPs on the ten upstream and ten downstream nucleosomes (black bars). Expected frequencies in the absence of regionality were estimated by re-assigning the SNEPs of this mark to random nucleosomes (red bars). Large black shoulders correspond to high regionality, where SNEPs tend to group together. Regionality of H3K4me3 remained when randomization was restricted to nucleosomes having above-background ChIP signal in at least one strain (Additional file 25, C). b SNEP frequency among +1, −1 and all other nucleosomes. Chi square test significance: **p value <10−6, *p value <0.01.