Example of digital differential display (DDD ), comparing gene expression between the liver (pool A) and heart (pool B) by comparing the available EST data from two Xenopus libraries. The top four results are shown. The numbers in grey represent the proportion of sequences within each pool that map to the UniGene cluster indicated in blue, for which a description is given on the right;cds, coding sequence. Dots are a visual representation of the numerical values. Statistically significant results are shown by indication of the relationship between two pools for a particular gene cluster, for example A > B for albumin and transferrin in the liver, B > A for myosin light chain and a probable actin homolog in the heart library.