After mitosis, each daughter cell contains the same number of chromosomes as the original parent cell. Mitosis is a fundamental type of cell division that produces two genetically identical daughter cells from a single parent cell. This process is essential for an organism’s growth, the repair of tissues, and asexual reproduction.
Chromosomes: The Genetic Blueprint
Chromosomes are structures within cells that organize genetic material, or DNA, containing the instructions for cell activity. These structures become visible as distinct, X-shaped forms during cell division. Most organisms have a characteristic number of chromosomes in their body cells, known as the diploid number (2n), with humans having 46 chromosomes, or 23 pairs.
Before a cell enters mitosis, its entire genetic material undergoes replication during a phase called interphase. This replication results in each chromosome consisting of two identical copies, called sister chromatids, which are joined together at a constricted region known as the centromere. Even though the DNA has doubled, a duplicated chromosome with two sister chromatids is still counted as a single chromosome. This duplication ensures that when the cell divides, each new cell receives a complete set of genetic information.
Mitosis: Ensuring Identical Copies
The process of mitosis unfolds through a series of stages that ensure accurate chromosome distribution. Initially, in prophase, the replicated chromosomes condense and become visible, while the nuclear envelope surrounding the DNA begins to break down. Structures called spindle fibers, made of microtubules, emerge from opposite poles of the cell and prepare to attach to the chromosomes.
During metaphase, the condensed chromosomes, each still composed of two sister chromatids, align along the cell’s central plane, known as the metaphase plate. Spindle fibers attach to a region on each centromere, called the kinetochore, connecting each sister chromatid to an opposite pole of the cell. This alignment ensures that each new cell receives an exact copy of every chromosome.
Anaphase then commences with the separation of the sister chromatids. Sister chromatids separate and move towards opposite ends of the cell. Once separated, each chromatid is considered an individual chromosome. The spindle fibers shorten, drawing these newly independent chromosomes to their respective poles.
Finally, in telophase, the chromosomes arrive at the poles and begin to decondense, returning to a less compact state. New nuclear envelopes form around each set of chromosomes, creating two distinct nuclei within the single cell. Concurrently, cytokinesis, the division of the cytoplasm, begins during late anaphase or telophase and fully separates the cell into two distinct daughter cells. This sequence of events ensures that each daughter cell receives a complete and identical set of chromosomes, maintaining the original chromosome number of the parent cell.