Final answer:
The start of centrosome duplication occurs during the prophase transition of cell division, which is a critical preparatory step for mitosis or meiosis.
Step-by-step explanation:
The start of centrosome duplication begins at the prophase transition. During prophase, the centrosomes, which are important for organizing microtubule growth, begin to move apart. Each centrosome, a pair of centrioles, starts to separate, and as they move to opposite ends of the cell, they create the mitotic spindle by extending microtubules between them. This process is crucial as it prepares the cell to enter prophase I of mitosis or meiosis with adequate apparatus for chromosomal manipulation and segregation.
Centrosome duplication is one of the key processes during prophase which sets the stage for the successful division of cells. As centrosomes migrate to two different sides of the cell, the microtubules, emanating from these centrosomes, start to form what is known as the mitotic spindle. These structures play an essential role in ensuring that sister chromatids or homologous chromosomes are correctly separated during the later phases of cell division.