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EOf centrioles, basal bodies and centrosomes What is the common thread linking the movement of spermatozoa, the sensing of light by our eyes and the cell-division apparatus of most of our cells? As implausible as it might seem, the structures that permit movement, light sensing and cell division are all made of microtubules, and are organized by the same organelle: the centriole or basal body (Fig. 1a). The presence of this nine-fold symmetri-cal structure in all branches of the eukaryotic ‘tree of life ’ led to the suggestion of its existence in the last common eukaryotic ancestor. The basal body/ centriole sets up the foundations for the axoneme, which forms the skeleton of cilia and fl agella; it also participates in the formation of the centrosome1 (Fig. 1a)