Mitosis is the biological process that allows a single cell to duplicate itself, serving as the basis for growth and the repair of damaged tissues. When a cell undergoes mitosis, the result is two new cells that are genetically identical to the parent cell. This duplication is achieved through a single, highly regulated sequence of events. Therefore, mitosis involves only one round of nuclear division and subsequent cellular division.
The Definitive Answer: Mitosis is a Single Division
The purpose of mitosis is to take a single parent cell, typically a diploid cell containing two sets of chromosomes, and divide it once to produce two new diploid daughter cells. This process is referred to as an “equational division” because the chromosome number in the daughter cells remains the same as the parent cell. The division event itself is singular, meaning the cell’s nucleus and cytoplasm split only one time.
A common point of confusion arises because the cell must prepare for this division by copying its genetic material. This DNA replication occurs during the S (synthesis) phase of the cell cycle, which happens before mitosis begins. This preparatory stage ensures that when the single division occurs, there are enough duplicated chromosomes to provide a full, identical set to each of the two resulting cells. The process is a single division of already-duplicated material, not two separate divisions.
Detailed Stages of Mitosis
The single round of division in mitosis is a continuous process broken down into four main stages, collectively known as karyokinesis, or the division of the nucleus. Prophase is the first step, marked by the condensation of chromatin into compact, visible chromosomes, each consisting of two identical sister chromatids. The mitotic spindle begins to form as the cell prepares to organize these chromosomes.
The next stage, metaphase, is characterized by the alignment of all the chromosomes along the cell’s central plane, known as the metaphase plate. This alignment ensures that each new cell will receive an exact copy of every chromosome. The single division begins its most active phase during anaphase, where the sister chromatids separate and are pulled to opposite poles of the cell by the shortening spindle fibers.
Telophase marks the final stage of nuclear division, as the separated sets of chromosomes arrive at the poles and begin to uncoil back into the less condensed chromatin state. A new nuclear envelope forms around each of the two chromosome sets, creating two distinct nuclei within the single parent cell. This nuclear division is followed by cytokinesis, the process where the cell’s cytoplasm physically divides to yield the two separate, identical daughter cells.
Why the Confusion? Mitosis vs. Meiosis
The idea that cell division involves two rounds is accurate, but it describes a different process called meiosis. Meiosis is the specialized type of cell division responsible for producing gametes, such as sperm and egg cells, required for sexual reproduction. The primary difference lies in the number of divisions and the resulting genetic outcome.
Meiosis is characterized by two successive division cycles, known as Meiosis I and Meiosis II, which occur after a single round of DNA replication. Meiosis I separates homologous chromosomes, while Meiosis II separates sister chromatids. This two-round process ultimately results in four daughter cells, each containing half the number of chromosomes of the parent cell, making them haploid.
In contrast to the genetically identical cells produced by mitosis, the four cells resulting from meiosis are genetically unique due to processes like crossing over that occur during the first round. Therefore, the confusion between one round and two rounds of division is a mix-up between mitosis, which is for growth and repair, and meiosis, which is for sexual reproduction.