Mitosis is a cellular process underpinning the growth and repair of most living organisms. It ensures a parent cell produces two genetically identical daughter cells. For somatic cells (body cells), mitosis maintains the diploid (2n) chromosome number. This consistent replication is important for cellular integrity and function.
What Do ‘n’ and ‘2n’ Mean?
The terms ‘n’ and ‘2n’ refer to the number of chromosome sets within a cell, known as ploidy. ‘n’ represents the haploid number, a single set of chromosomes. Cells with this single set, like gametes (sperm and egg cells), are haploid. These cells are specialized for sexual reproduction, each carrying half the genetic information for a new organism.
Conversely, ‘2n’ denotes the diploid number, meaning a cell contains two complete sets of chromosomes. One set is inherited from each parent, forming homologous pairs. Most somatic cells (body cells) in humans are diploid, containing 46 chromosomes (2n = 46), with 23 from each parent. Diploid cells are the basis for growth, tissue maintenance, and repair in multicellular organisms.
Ploidy Through Mitosis
Mitosis is an equational division, preserving the chromosome number from parent to daughter cells. Before mitosis, during interphase, the cell undergoes DNA replication. In this S phase, each chromosome duplicates, resulting in two identical sister chromatids. Although DNA content doubles, the chromosome number remains 2n because sister chromatids are attached and counted as a single chromosome.
As mitosis progresses, these duplicated chromosomes align at the cell’s center. The sister chromatids then separate and are pulled to opposite ends by spindle fibers. This separation ensures each new nucleus receives a complete and identical set of chromosomes. Finally, the cell divides, resulting in two daughter cells, each with the same 2n chromosome number as the original parent cell.
Mitosis Versus Meiosis and Ploidy
While both mitosis and meiosis are forms of cell division, they serve distinct biological purposes regarding ploidy. Mitosis, an equational division, produces two diploid (2n) daughter cells genetically identical to the parent. This process involves a single round of nuclear division after DNA replication.
Meiosis, in contrast, is a reductional division that halves the chromosome number. It occurs in germ cells to produce gametes (sperm and egg cells). Meiosis involves one round of DNA replication followed by two successive cell divisions, yielding four haploid (n) daughter cells. These haploid cells are genetically unique due to processes like crossing over, which introduces genetic variation.
Why Mitosis Matters
The preservation of the 2n ploidy level through mitosis is important for the health and continuity of multicellular life. A primary function is organismal growth, where repeated mitotic divisions increase cell numbers while maintaining genetic consistency throughout the developing organism. This allows a single fertilized egg to develop into a complex multicellular individual.
Mitosis also plays an important role in tissue repair and regeneration. When cells are damaged, old, or worn out, mitosis ensures they are replaced with new, genetically identical cells, preserving tissue structure and function. Examples include the constant replacement of skin cells or the healing of wounds. In some organisms, mitosis is also the basis for asexual reproduction, allowing them to produce genetically identical offspring from a single parent.