During which phase do chromosomes duplicate?

Chromosomes duplicate during interphase, which is the phase of the cell cycle where the cell prepares for division. Interphase consists of three stages: G1 (first gap), S (synthesis), and G2 (second gap). It is specifically in the S phase of interphase that DNA replication occurs, leading to the duplication of chromosomes. As a result, each chromosome consists of two sister chromatids, which are identical copies that will be separated during cell division.

In contrast, prophase is the phase where the chromosomes condense and become visible, but it is not the stage where they duplicate. Anaphase is when the sister chromatids are pulled apart to opposite sides of the cell, and telophase involves the reformation of the nuclear envelope around each set of separated chromosomes. Therefore, interphase, particularly the S phase, is the critical time for chromosome duplication.