Here's why:
* The Cell Cycle: Cells go through a cycle of growth and division. This cycle has several phases:
* G1 Phase: The cell grows and carries out its normal functions.
* S Phase: The cell replicates its DNA, doubling the number of chromosomes.
* G2 Phase: The cell prepares for mitosis (cell division), ensuring all necessary proteins and organelles are present.
* M Phase: The cell divides its nucleus (mitosis) and cytoplasm (cytokinesis).
* Chromosome Doubling: During the S phase, each chromosome replicates, creating two identical copies called sister chromatids. These sister chromatids remain attached at a region called the centromere.
* G2 Phase: After S phase, the cell enters G2. This phase is where the cell "checks" that DNA replication was successful and makes sure it has enough resources for division. While the chromosomes are already duplicated, they stay condensed until the onset of mitosis (M phase).
So, in G2 phase, each chromosome has been doubled into two sister chromatids, but they are still attached, making the cell's total genetic material double what it was at the start of the cycle.
