Figure 3. Variation in gene expression. These bar charts summarize data for Gpnmb and Chf across 103 strains, with strain names or numbers along the x-axis (BXD1 is abbreviated 01). The y-axis indicates expression on a log2 scale. Bars are standard errors of the mean. A: Variation in gene expression of the glaucoma gene Gpnmb (probe set 1448303_at) indicates that fifteen BXD strains have low expression and can be used as models for glaucoma, retinal ganglion cells degeneration, and defects of innate immunity [80]. The 25-fold decrease in expression of Gpnmb in DBA/2J and 15 of the new BXD strains (left side) is caused by a mutation that introduces a premature stop codon in the middle of exon 4 (R150X, CGA to TGA, Chr 6 nucleotide 48.974971 Mb) [10,80]. This mutation eliminates the target region of the transcript and enhances nonsense-mediated RNA decay of the truncated transcript. This variation in expression maps as a strong cis QTL. B: There is a 2.6 fold range of expression of complement factor H (Cfh), probe set 1423153_x_at) this is determined by generating bar charts of strain variation in gene expression. How to generate bar charts of strain variation in gene expression. Step 1. Work through the steps described in Figure 1 using Gpnmb as the search term in Step 1. Step 2. Once you have opened the Trait Data and Analysis Form shown in Figure 4 below, select the 'Basic Statistics' button.