Copyright information:Taken from "Phylogenetic analysis of Shiga toxin 1 and Shiga toxin 2 genes associated with disease outbreaks"http://www.biomedcentral.com/1471-2180/7/109BMC Microbiology 2007;7():109-109.Published online 4 Dec 2007PMCID:PMC2211750.w (1 and 2) indicate a d:dratio of > 1 or positive selection. Any shade of bordeaux (4–7) indicates a d:dratio of < 1 or purifying selection.