species by comparing their homologous genes and looking for common patterns of collinearity on a chromosomal or contig scale. Homologies are usually determined on the basis of high bit score BLAST hits that occur between multiple genomes. From here, dynamic programming is used to select the best scoring path of shared homologous genes between species, taking into account potential gene loss and gain which may have occurred in the species' evolutionary histories. See also Ridge (biology) Ultra-conserved element Comparative genomics References External links ACT (Artemis Comparison Tool) — Probably the most used synteny software program used in comparative genomics. Comparative Maps NIH's National Library of Medicine NCBI link to Gene Homology resources, and Comparative Chromosome Maps of the Human, Mouse, and Rat. Graham Moore group research page - cereal genomics More information on synteny and its use in comparative cereal genomics. NCBI Home Page NIH's National Library of Medicine NCBI (National Center for Biotechnology Information) link to a tremendous number of resources. SimpleSynteny A free browser-based tool to compare and visualize microsynteny across multiple genomes for a set of genes. Synteny server Server for Synteny Identification and Analysis of Genome Rearrangement—the Identification of synteny and calculating reversal distances. PlantSyntenyViewer A web based visualisation tool allowing to navigate on genomes and visualizing the Synteny conservation among several datasets (cereals, dicotyledons, animals, a Wheat-based one...) Bioinformatics Classical genetics