A student says: 'When a cell divides by mitosis, the DNA must be copied before division can occur.' Explain why the student is correct, and describe what happens to the chromosomes during mitosis to ensure each daughter cell receives the correct genetic information.

DNA is replicated during the S‑phase of the cell cycle, before mitosis begins. This duplication gives each chromosome a sister chromatid, so that a full set of genetic material is available for the two future cells.

During mitosis the duplicated chromosomes line up at the metaphase plate (the cell’s equator). In anaphase the sister chromatids are pulled apart by spindle fibres to opposite poles of the cell. Finally, cytokinesis separates the cytoplasm, producing two daughter cells, each with the same number of chromosomes as the original cell and therefore genetically identical to it.