Mitosis Animation

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Mitosis Animation

Mitosis Animation
Mitosis Animation. Animation courtesy of Tom Diab. Used with permission.

Mitosis Animation

Mitosis or cell division is a process that enables organisms to grow and reproduce. Dividing cells go through an ordered series of events called the cell cycle. Mitosis is a phase of the cell cycle in which the genetic material from a parent cell is divided equally between two cells. Before a dividing cell enters mitosis, it must duplicate its genetic material and increase its organelles and cytoplasm. This period of growth is called interphase. Interphase is composed of three phases: G1 phase, S phase, and G2 phase. The G1 phase is the period prior to the synthesis of DNA. The S phase is the the period during which DNA is synthesized and the G2 phase is the period after DNA synthesis has occurred but prior to the start of the first mitotic phase. In animal cells, two pair of centrioles formed from the replication of one pair are also located outside of the nucleus during interphase.

There are several phases or steps in mitosis. These stages are:

  • Prophase
  • Metaphase
  • Anaphase
  • Telophase

Mitosis Phases

The animation above illustrates the different phases of mitosis in a plant cell. The following changes occur in the different phases of mitosis.

Prophase

In prophase, changes occur in both the cytoplasm and nucleus of the dividing cell. The chromatin condenses into discrete chromosomes. The chromosomes begin to migrate toward the cell center. The nuclear envelope breaks down and spindles form at opposite poles of the cell. In animal cells, the mitotic spindle initially appears as structures called asters which surround each centriole pair.

Metaphase

In metaphase, the nuclear membrane disappears completely. The spindle fully develops and the chromosomes align at the metaphase plate (a plane that is equally distant from the two poles). Chromosomes are held at the metaphase plate by the equal forces of the polar fibers pushing on the centromeres of the chromosomes. In animal cells, two pair of centrioles align at opposite poles of the cell.

Anaphase

In anaphase, the paired chromosomes (sister chromatids) separate and begin moving to opposite ends (poles) of the cell. Spindle fibers not connected to chromatids lengthen and elongate the cell. Once the paired sister chromatids separate from one another, each is considered a full chromosome. They are referred to as daughter chromosomes. In preparation for the next stage of mitosis, the two cell poles also move further apart. At the end of anaphase, each pole contains a complete compilation of chromosomes.

Telephase

In telephase, the chromosomes are cordoned off into distinct new nuclei in the emerging daughter cells. The polar fibers continue to lengthen and nuclei begin to form at opposite poles. At the end of telophase, the genetic content of the cell is divided equally into two parts. Cytokinesis, the division of the original cell's cytoplasm, begins prior to the end of mitosis and completes shortly after telophase. In animal cells, proteins actin and myosin work to divide the cell in two. In plant cells, a cell plate forms at the metaphase plate, separating the two daughter cells. At the end of mitosis, two distinct cells with identical genetic material are produced. If the dividing cell is haploid, each cell will have one complete set of chromosomes. If the dividing cell is diploid, each cell will have two complete sets of chromosomes.

Meiosis

Organisms that reproduce sexually undergo a type of cell division called meiosis. Through a sequence of steps, the replicated genetic material in a parent cell is distributed among four daughter cells. Meiosis is very similar to the process of mitosis, yet it is also fundamentally different. There are two stages of meiosis: meiosis I and meiosis II. At the end of meiosis I, two daughter cells are produced. At the end of meiosis II, four daughter cells are produced, each with one half the number of chromosomes as the original parent cell.