The Genome Browser database contains genome sequence from GenBank (3) for a wide selection of organisms, many with multiple assembly versions. In September 2013 our database included 13 primates, 33 additional mammals, 17 non-mammalian vertebrates, 13 insects, 6 worms and 5 other invertebrates. Annotation data for each genome assembly are displayed graphically as ‘tracks’ aligned to the genomic sequence and grouped according to shared characteristics, such as gene predictions or comparative genomics. The level of annotation varies among organisms. At a minimum, most assemblies offer mapping and sequence annotation tracks describing assembly, gap and GC content, and alignments of mRNA, EST and RefSeq (3) genes (available on approximately one-half of the assemblies) from GenBank. Some assemblies provide additional gene annotation tracks, such as Ensembl Genes (4) and Human Proteins, as well as multiple sequence alignments (multiz) (5) and pairwise genomic alignments between assemblies to facilitate comparative and evolutionary investigations. The heavily annotated human genome offers extensive conservation and evolutionary comparisons, a large collection of gene models including the locally generated UCSC Genes track (6,7), regulation, expression, epigenetics and tissue differentiation,
