The number of DNA molecules in one chromosome depends on the cell cycle stage.
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In a non-dividing cell (G1 phase): Each chromosome consists of one DNA molecule. This single DNA molecule contains the genes for that chromosome.
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In a dividing cell (after DNA replication in S phase, during G2 phase and mitosis): Each chromosome consists of two identical DNA molecules. These two identical DNA molecules are called sister chromatids, held together at the centromere. After cell division, the sister chromatids separate, and each daughter cell receives one DNA molecule per chromosome.
In summary:
| Cell State | Number of DNA Molecules per Chromosome |
|---|---|
| Non-Dividing | 1 |
| After Replication | 2 (sister chromatids) |
