Chromosomes are structures found within the nucleus of cells. They carry deoxyribonucleic acid (DNA), which holds the genetic instructions for an organism’s development and function. Chromosomes also contain proteins that help organize and package the DNA, allowing it to fit inside the cell. A typical human cell contains 23 pairs of chromosomes, totaling 46. This set includes 22 pairs of autosomes, carrying most genetic traits, and one pair of sex chromosomes, determining biological sex.
Understanding Cell Division: Mitosis
When a human cell divides for growth or repair, it undergoes mitosis. This type of cell division is how most body cells (somatic cells) reproduce, creating new cells genetically identical to the original parent cell. Before mitosis, the cell enters a preparatory stage known as interphase. During interphase, the cell duplicates its entire set of DNA.
Each of the 46 chromosomes creates an exact copy, forming two sister chromatids. These sister chromatids remain joined at the centromere. Despite the DNA doubling, the cell’s chromosome count remains 46 at this stage because each pair of joined sister chromatids is considered a single chromosome unit. Mitosis then unfolds through distinct phases: prophase, metaphase, anaphase, and telophase.
In prophase, duplicated chromosomes condense and become more compact, making them visible under a microscope. In metaphase, these condensed chromosomes align along the cell’s middle, and the mitotic spindle, made of protein fibers, attaches to each chromosome. In anaphase, sister chromatids separate and are pulled by spindle fibers to opposite ends of the dividing cell. In telophase, a new nuclear membrane forms around each set of chromosomes. The cell then divides into two daughter cells through cytokinesis.
The Outcome of Human Cell Division
After a human cell completes mitosis, it divides into two daughter cells. Each daughter cell contains an exact copy of the genetic material from the original parent cell. This means each daughter cell possesses 46 chromosomes. This precise distribution ensures that genetic information is consistently passed on from one cell generation to the next, maintaining genetic stability.
Why Maintaining Chromosome Number Matters
Maintaining a consistent chromosome number through mitosis is important for multicellular organisms. This process enables growth, allowing an organism to develop from a single cell into a complex being by generating new cells. It is also important for tissue repair, continuously replacing old or damaged cells.
When errors occur during cell division, they can result in daughter cells with an incorrect number of chromosomes, known as aneuploidy. Such chromosomal imbalances disrupt normal cell processes, leading to protein imbalance and impaired cellular functions. These abnormalities are detrimental to cell health and can be associated with health challenges, including developmental issues and diseases like cancer.