Summary of the gene expression patterns associated with sporozoite-initiated development. The relative timeline of sporozoite to bradyzoite development is indicated at the top of the diagram. Sporozoite- and bradyzoite-specific gene expression clearly demarcates these stages, while tachyzoite-specific patterns are more fluid with respect to developmental phenotypes. Gene expression patterns in Day-6 and RH parasites are highly correlated; however, the maximum tachyzoite antigen expression based on overall SAGE tag frequencies was observed in the Day-7 population. All laboratory strains are placed in the timeline on the basis of a best-fit criterion. Alkaline-shifted parasites (pH-shifted) express all the known bradyzoite genes, and are therefore considered to be nearly identical to mature bradyzoites in this diagram.