Mitosis is a fundamental biological process where a single cell divides to produce two genetically identical daughter cells. This cell division is crucial for the growth of multicellular organisms, the repair of damaged tissues, and the replacement of old cells.
What Chromosomes Are
Chromosomes are structures located inside the nucleus of nearly every cell, acting as organized packages of deoxyribonucleic acid (DNA). This DNA contains an organism’s genes, which are the instructions for building and operating a cell. Human cells typically contain 46 chromosomes, arranged in 23 pairs, with one chromosome from each pair inherited from each parent.
Before Mitosis Begins
Cells undergo a preparatory period known as interphase before mitosis. During the synthesis (S) phase, the cell replicates its entire DNA content. Each chromosome is duplicated to form two identical copies called sister chromatids, which remain attached at a central point called the centromere. Despite DNA doubling, the chromosome count does not change; a chromosome with two sister chromatids is still considered a single chromosome. A human cell preparing for mitosis therefore has 46 chromosomes, each consisting of two sister chromatids.
Chromosome Behavior During Mitosis
As a cell proceeds into mitosis, the behavior of its chromosomes is precisely coordinated across several stages. In prophase, the replicated chromosomes, each composed of two sister chromatids, condense and become visible. At this stage, the human cell still contains 46 chromosomes, each with its duplicated genetic material. In metaphase, these condensed chromosomes align along the cell’s central plane, forming the metaphase plate. The chromosome count remains at 46, with each still consisting of two sister chromatids.
During anaphase, the centromeres holding the sister chromatids together divide, allowing them to separate. Once separated, each chromatid is considered an individual chromosome. These individualized chromosomes are pulled to opposite ends of the cell. This temporary separation doubles the chromosome count within the cell to 92, as each of the original 46 duplicated chromosomes effectively becomes two distinct chromosomes moving apart.
In telophase, the chromosomes arrive at the cell’s poles and begin to decondense. New nuclear envelopes form around each set of chromosomes. Each forming nucleus now contains 46 individual chromosomes, restoring the original chromosome number.
The Outcome of Mitosis
Mitosis culminates in the formation of two new daughter cells through cytokinesis, which divides the cytoplasm. Each daughter cell is genetically identical to the original parent cell. Each new daughter cell receives the same number of chromosomes as the parent cell began with. For human cells, this means each daughter cell inherits a complete set of 46 chromosomes. This precise distribution maintains genetic stability, supports growth, and enables tissue repair.