Figure 4.  Muscle gene positions are clustered in small groups of two to five genes along the chromosomes. A. Histogram comparing the results of 10,000 random samples with the observed number of clustered muscle genes (red arrow).  B. The distribution of the number of muscle-expressed genes in each cluster. C. Schematic of 0.7 Mb of chromosome V, showing the positions of all genes (black vertical lines), and genes expressed in muscle (red vertical lines).