Fig. 6

Strain-specific expression bias at genes around non-imprinted Zfp57 peaks. Allelic activity and expression level for eight genes found to have significant allelic bias in hybrid ES cells (ES, clear dots) and their neural stem cell derivatives (NS, filled dots); see also Fig. S10 in Additional file 1 and Table 3. The corresponding genomic DNA standard (expected 50 % allele composition) used to control for PCR bias and pyrosequencing artifacts is shown as a fitted linear regression (red dotted line). Allelic composition found by SNP pyrosequencing is plotted along the y-axes as percentage of BL6 expression (0 % = pure Cast, 100 % = pure BL6 and 50 % = perfect biallelic) and overall expression level by quantitative RT-PCR is plotted along the x-axes as absolute levels of the control hybrid genomic DNA (log2 nanograms/PCR). The title in each graph shows gene name and closest associated ZFP57 peak along with its relative position with respect to the gene. Note that for Sdk2 a dilution series of neural stem cell cDNA (high level biallelic expression) was used as a control since the relevant exon boundary panning primers could not amplify genomic DNA