Your body is constantly renewing itself. Skin cells flake off, tissues heal after an injury, and you grow from a single fertilized egg into a complex organism. The process powering all of this is mitosis, a type of cell division that produces two genetically identical daughter cells from a single parent cell.

Mitosis is a fundamental part of the cell cycle. After a period of growth and DNA replication known as interphase, the cell is ready to divide. The main goal of mitosis is to accurately separate the duplicated genetic material, ensuring that each new cell gets a perfect copy of the original's DNA.

Think of it as cellular photocopying. This process is essential for multicellular organisms to grow, maintain tissues, and repair damage. When you get a paper cut, mitosis is what creates new skin cells to seal the wound.

Though it's a continuous process, biologists divide mitosis into four distinct stages based on the appearance and behavior of the chromosomes. A common way to remember the order is with the acronym PMAT.

Here is a brief overview of each stage:

• Prophase: The cell's DNA, normally loose, condenses into visible, X-shaped structures called chromosomes. Each chromosome consists of two identical sister chromatids joined together. The nuclear envelope, which encloses the DNA, starts to break down.
• Metaphase: The chromosomes align in a single file line at the center of the cell, an area known as the metaphase plate. Microscopic fibers called spindles attach to each chromosome, ready to pull them apart.
• Anaphase: The spindle fibers shorten, pulling the sister chromatids apart. Each chromatid is now considered its own chromosome. They move to opposite poles of the cell, ensuring each new cell will get a complete set.
• Telophase: The chromosomes arrive at opposite poles and begin to decondense, returning to their stringy form. A new nuclear envelope forms around each of the two sets of chromosomes, creating two distinct nuclei within the single cell.

Mitosis is technically just the division of the nucleus. The process that divides the rest of the cell, the cytoplasm, is called cytokinesis. It typically begins during late anaphase or telophase.

In animal cells, the cell membrane pinches inward, creating what's called a cleavage furrow, until the cell splits into two. Plant cells, with their rigid cell walls, form a new structure down the middle called a cell plate, which develops into a new cell wall separating the two daughter cells.

At the end of mitosis and cytokinesis, what started as one cell has become two smaller, but genetically identical, daughter cells. These cells can then enter their own cycle of growth and, eventually, division.

Ready to check your understanding?

Understanding mitosis is the first step in grasping how complex life forms grow, develop, and heal.