How can one cell divide into two with chromosome copies?

One cell can divide into two while passing a chromosome complement to each new cell. Chromosomes are structures containing DNA and associated proteins. Before an ordinary mitotic division, the DNA is copied so that separation can distribute copies rather than split one unprepared set between two cells.

In the example, the starting cell has two schematic chromosomes. DNA replication makes two attached copies for each. These copies are sister chromatids. The joined pair still counts as one replicated chromosome until its sister chromatids separate, so chromosome number and DNA-molecule number are not interchangeable.

During mitosis, the duplicated material is organized and the sister chromatids separate toward opposite ends of the cell. Each separated chromatid is then a chromosome. The intended result is a chromosome complement at each end, not half of the original information randomly left behind.

Cytokinesis is the division of the cell contents into daughter cells. After it, the illustrated division has produced two cells, each with two chromosomes. The sequence separates preparation from distribution: DNA copying comes before mitosis, while division of the cell completes the pictured result. It is not the meiotic process that produces four haploid products.