Poisson model-based clustering analysis for photoreceptor gene expression using 10 clusters. SAGE libraries are plotted on the x-axis. Numbers one to fourteen represent the fourteen SAGE libraries mentioned in Method Section, i.e. 1: hypo; 2: 3t3; 3: E12.5; 4: 14.5; 5: E16.5; 6: E18.5; 7: P0.5; 8: P2.5; 9: P4.5; 10: P6.5; 11: P10.5Crx-/-; 12: P10.5Crx+/+; 13: Adult; 14: ONL. Tag abundance is shown on the y-axis. Data were normalized before plotting. Each tag from the 14 libraries was rescaled to make the sum of the expression values equal to one. Different colors represent different tags.