Centrosome duplication during the cell cycle. (A) Centrosomes are comprised of two centrioles (mother and daughter) connected via an interconnecting fiber. The mother centriole has additional distal and sub distal appendages. The centrioles are surrounded by a matrix of proteins, the pericentriolar material (PCM). (B) During the cell cycle, each centriole (the original mother and daughter centriole) duplicates once, growing a new daughter centriole from their sides. The original mother centriole duplicates at a faster rate than the original daughter centriole. The original daughter centriole acquires additional appendages and thus becomes a new mother centriole. Mitosis separates the two centrosomes (duplicated centrioles) resulting in two cells each with a differentially aged mother centriole. Differences between these cells regarding cell fate and regulation are beginning to emerge.