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The centrioles and centrosomes duplicate during the G2 this has not occurred during the S phase. The centrosomes are the while "glowing" spheres. These are the organizing centers and anchors for the microtubules (spindle fibers). All eukaryotes have centrioles except plants. Centrioles function as the basal organizing center of cilia and flagella. Plants produce no cells with either cillia or flagella. Tje centrioles appear to ride on top of/attached to the centrosomes. Tubulin is also synthesized and microtubules begin forming during the G2 phase. The spindles begin developing in the S phase and appear as an aster. You know/will learn the rest of the spindle/micotubule story during mitosis. |