A centriole is a specialized organelle, also called a cell body, which is found in the cells of most animals. Centrioles are roughly tubular in shape, and they play an important role in cell division. These cell structures are so tiny that their details cannot be seen without the assistance of an electron microscope; during cell division, the activity of the centrioles can clearly be seen under an electron microscope.

Centrioles are among the many organelles which help a eukaryotic cell to run smoothly. A eukaryotic cell is a complex cell with a number of miniature cellular organs which all serve different functions. A eukaryotic cell also has a cell nucleus and a complex physical structure which sets it aside from prokaryotic cells like those of bacteria. Humans, among other animals, are made from eukaryotic cells, and these cells periodically divide to renew themselves so that their larger hosts can grow and remain healthy.

In an animal with centrioles, each cell has a pair of centrioles. The shape of these organelles is actually quite fascinating and beautiful; they consist of nine triplets of microtubules arranged in a pinwheel shape around a central cylinder. The two pairs collectively make up a structure in the cell which is called the centrosome, with one centriole aligned in an orientation which is perpendicular to the other. The centriole is at the core of cell division.

When a cell divides, the centrosome replicates itself, forming two centrosomes which move to opposite ends of the cell. Each centrosome then sends out spindles which are supposed to separate the cell's DNA, differentiating a cell into two copies of itself which can then split into fresh cells. An error during this process can create a mutated cell, which may harmlessly die off or become more malignant, depending on the mutation.

The existence of the centrosome, by the way, was discovered by Theodor Boveri in 1888, and Boveri also put forward an early theory that cancer was caused by errors during cell division. Although mocked at the time, Boveri was later proved correct. In addition to playing an important role in cell division, a centriole also helps to provide structural support for its parent cell. It would also appear that a centriole has its own unique genetic code which is distinct from the code of the cell; scientists believe that this code allows the centrosome to divide and carry out its various functions in the cell.