Links from the Xenopus Anatomy Ontology to Xenopus data in Xenbase. The XAO search anatomy items function returns the exact match on the query term 'heart’. In addition, anatomy features such as 'cardiac mesoderm’ that have relationships to 'heart’ in the ontology are also returned. Clicking on any term takes users to an XAO term summary page. The Expression tab on the 'heart’ term page has links to data related to 4520 expressed genes. Shown schematically is a sample of genes (green fill) that most frequently appear in each of three principal data categories (images, clones, papers: indicated by solid lines). nkx2-5 expression appears in the greatest number of Xenbase images and is cited in the most publications. The gene acta1 is associated with the most clones from heart tissue. The genes actc1, myl3 and acta1 (bold outline) are associated with the greatest combined number of records as of May 20, 2013. The total number of records in each data category for all heart-expressed genes is shown. Heart image by Kolker, Tajchman & Weeks , used with permission, ©Elsevier (2000).