|Glyceraldehyde-3-phosphate dehydrogenase genes of N=134 bacterial species, arranged in order of gene G+C content (high GC at the top). Hot colors are G and C. Cool colors are A and T.
What are we looking at? This is actually a composite rendering of the glyceraldehyde-3-phosphate dehydrogenase genes (DNA sequence info) from 134 bacterial species. Each gene is painted left-to-right (5' to 3') in a strip 4 pixels tall, with hot colors assigned to DNA bases G and C (guanine and cytosine), and cool colors assigned to bases A and T (adenine and thymine). Wherever there's a G or C, it gets painted red or red-orange. Wherever there's A or T, blue or blue-green. Same gene, 134 versions, varying significantly in G+C content. (The gene GC content ranges from a maximum of 69.2% at the top to 29.4% at the bottom.)
Why glyceraldehyde-3-phosphate dehydrogenase (GAPDH)? No real reason, except that it's a fairly universal (indeed, quite ancient) metabolic enzyme, reasonably compact (making possible a rendering that's not super-wide, as it would be for a larger gene), well-delineated genetically (not a fusion protein or an enzyme with multiple isoforms), and probably representative of a good many core metabolic enzymes. This is the enzyme that catalyzes the sixth step of glycolysis (sugar-breakdown). You may recall from Biochem 101 that the breakdown of glucose proceeds by splitting the twice phosphorylated molecule into two 3-carbon pieces. The triose phosphates in turn get phosphorylated by GAPDH before they transfer a phosphate to ADP to yield ATP, the 5-hour energy drink of all cells everywhere.