Mitosis is the process of cell division that results in two daughter cells genetically identical to the parent cell, which is used for growth, repair, and asexual reproduction. Chromosome number is defined by ploidy. A haploid cell contains a single set of chromosomes, designated as n. In contrast, a diploid cell contains two sets of chromosomes, one set inherited from each parent, designated as 2n. Although the most familiar examples of mitosis involve diploid cells, haploid cells routinely undergo mitosis in many different life forms.
Understanding Haploid and Diploid States
In humans and most animals, nearly all body cells, known as somatic cells, are diploid (2n). These diploid cells contain two complete sets of chromosomes. Mitosis in these cells maintains the 2n state, producing two new cells for tissue maintenance or growth.
The only haploid cells (n) in the human body are the specialized reproductive cells, or gametes, such as sperm and eggs. These are created through meiosis, which reduces the chromosome number by half. Meiosis is necessary so that when two gametes fuse during fertilization, the resulting zygote restores the organism’s characteristic diploid number.
The Mechanics of Haploid Mitosis
Mitosis is fundamentally a process of duplication and separation, and its mechanism is structurally the same in both haploid and diploid cells. Before division, the cell must replicate its single set of chromosomes during the S-phase, so that each chromosome consists of two identical sister chromatids.
The subsequent phases—Prophase, Metaphase, Anaphase, and Telophase—unfold exactly as they do in a diploid cell. During Metaphase, the replicated chromosomes align individually along the central plate. The critical step occurs in Anaphase, where the sister chromatids separate and are pulled toward opposite ends of the cell by the spindle fibers.
The result is two daughter cells, each containing one full set of chromosomes, meaning they are haploid (n) and genetically identical to the original parent cell. The process is simpler than diploid mitosis because there are no homologous chromosome pairs to manage.
Biological Context: Where This Division Occurs
Haploid mitosis is the dominant form of cell division in numerous organisms and life cycle stages. Many fungi and algae spend the majority of their lives as multicellular haploid organisms, using mitosis for growth, development, and asexual reproduction.
In the plant kingdom, haploid mitosis is central to the alternation of generations. The haploid stage, known as the gametophyte, uses mitosis to grow from a spore into a multicellular structure. The gametophyte then uses mitosis again to produce gametes, which is a distinct difference from animals where gametes are formed by meiosis.
A striking animal example is found in male honey bees, known as drones. Drones develop from unfertilized eggs and are haploid their entire lives. Since they possess only one set of chromosomes, they cannot undergo meiosis, which requires homologous pairs to halve the genetic material. Instead, drones produce their sperm cells exclusively through mitosis, resulting in sperm that are genetically identical to the drone itself.