Toxoplasma gondii is a member of the phylum Apicomplexa, a diverse group of early branching eukaryotes related to dinoflagellates and ciliates (see Chapter 12; Baldauf, 2003). The definitive host is the cat where the sexual cycle takes place in the intestinal epithelia and oocysts are shed in the feces where meiosis occurs to produce environmentally resistant sporozoites (see Chapter 1). The life cycle is unusual compared to closely related coccidians in that the parasite can transmit directly between secondary hosts. This has allowed donal growth and expansion in the population where the vast majority of isolates in North America and Europe are dominated by three clonal lineages (Howe and Sibley, 1995). Moreover, the predominance of the three clonal lineages appears to have emerged from a population bottleneck about 10 000 years ago (Su et al., 2003) where the lineages appear to be derived from just a few related ancestral strains (Grigg et al., 2001a). T.gondii in South America appear to be more divergent but a greater analysis of isolates is required. Genetic mapping and sequence analysis reveals an ~65Mb genome distributed across 14 chromosomes which is over twice the size of Plasmodium Jalciparum (Khan et al., 2005). This difference is due to higher predicted gene content, lower gene density and more introns per gene. The genome annotation shows that compared to P.jalciparum, T. gondii retains many more enzymes in carbohydrate, lipid, amino acid and nucleic acid metabolic pathways (see Chapters 19 and 20).
|Title of host publication||Toxoplasma|
|Subtitle of host publication||molecular and cellular biology|
|Editors||James W. Ajioka, Dominique Soldati|
|Place of Publication||Norfolk, England|
|Number of pages||15|
|Publication status||Published - 2007|
Khan, A., Taylor, S., Su, C., Sibley, L. D., Paulsen, I., & Ajioka, J. W. (2007). Genetics and genome organization of Toxoplasma gondii. In J. W. Ajioka, & D. Soldati (Eds.), Toxoplasma: molecular and cellular biology (pp. 193-207). Norfolk, England: Horizon Bioscience.