(A) Schematic of a metaphase centrosome containing a mature mother centriole that can recruit pericentriolar material and reproduce, and her immature daughter centriole. The pericentriolar material recruited by the mother centriole nucleates microtubules and organizes the pole of the mitotic spindle. (B) The steps in the assembly and maturation of the daughter centriole are illustrated, along with the proteins required for each step. Schematics on the bottom show a cross-sectional view of the daughter. Assembly begins when a cartwheel (grey) forms at a right angle to the mother centriole. In the second step, an outer wall made up of nine symmetrically-arranged microtubules (grey) forms around the cartwheel. Assembly of the paddlewheel (a set of protrusions that run along the length of each microtubule; red) and acquisition of the ability to reproduce requires SAS-7. (C) The phenotypes observed when a sperm cell containing a wild-type pair of centrioles fertilizes a wild-type egg cell (left column), an egg cell lacking a component essential for daughter centriole formation (middle column), or an egg cell lacking a component required for daughter centrioles to acquire the ability to reproduce (right column).