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Big Picture

Cell division: mitosis and cytokinesis

Accurate cell division is essential for organisms to repair themselves and grow, so the process is very tightly controlled. We've put together a gallery of 19 images to show what happens during the cell division (or M phase) of the cell cycle, which consists of mitosis and cytokinesis.

Before a eukaryotic cell can divide it needs to replicate (copy) all of its DNA, so that the daughter cells produced will both contain the same genetic information. This process of nuclear division is known as mitosis. There are several different stages of mitosis: interphase, prophase, metaphase, anaphase and telophase, each of which can occur only when the stage preceding it is complete.

Once telophase has finished, the cell has double the normal amount of genetic information and is ready to divide. The separation of the cytoplasm and the organelles into two identical 'daughter' cells is called cytokinesis.

Image research and captions by Laura Pastorelli. For more scientific and medical images, see Wellcome Images.

Mitosis in onion cells
Mitosis in onion cells
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Light microscopy image showing the process of cell division in onion root cells. This is a vertical section taken from an area of onion root. This particular region is the undifferentiated region of plant tissue from which new cells are formed and is, therefore, an area of high cell division. The cells in this image are in various stages of mitosis: the top layer of cells are all in interphase (the stage of DNA replication). The second layer down shows two cells (central) in prophase (the stage at which DNA condenses into chromosomes and the mitotic spindle begins to form). The third row down has a cell (second from the right) in early anaphase (chromosomes clearly attached to spindle and seen moving towards opposite poles) and two cells that have just divided. In some cells there appears to be no nucleus. This is due to the way in which the section of tissue was cut, which meant the nucleus is not visible or is smaller in some cells.
Credit: Spike Walker, Wellcome Images.
Human cells showing the stages of cell division
Human cells showing the stages of cell division
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Fluorescence micrograph showing human cells at various stages of cell division, starting with interphase at the top. During interphase the cell gets bigger and duplicates its DNA. The second cell shows prophase, the stage at which the chromosomes form. The third cell is in metaphase, where all the chromosomes are attached and aligned on the spindle. The fourth cell down shows anaphase, the stage at which the chromosomes separate. The final cell is in telophase, and the newly separated genetic material is encased into two new nuclei.
Credit: Matthew Daniels, Wellcome Images.
Human HeLa cancer cells at different stages of mitosis
Human HeLa cancer cells at different stages of mitosis
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Fluorescence micrograph showing HeLa (human cancer) cells during the stages of mitosis. The microtubules of the cytoskeleton/spindle are fluorescing red, the DNA (chromosomes) green. The stages shown are (clockwise from the top):prophase, prometaphase, metaphase, anaphase, telophase, cytokinesis, end of cytokinesis, interphase.
Credit: Individual scientists, University of Dundee, Wellcome Images.
Human chromosomes at three stages of mitosis
Human chromosomes at three stages of mitosis
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Fluorescence micrograph showing human chromosomes (blue) at three stages of mitosis (from the left): metaphase, anaphase and telophase. Centromeres (condensed regions of DNA at the centre of chromosomes) are shown in green, and the mitotic spindle is labelled red.
Credit: Laura Trinkle-Mulcahy, Wellcome Images.
Illustration of a cell at prophase
Illustration of a cell at prophase
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Computer-generated illustration showing a cell at prophase. During prophase, the cell prepares the equipment it needs to separate its genetic material. The cell has completed interphase, which means that the DNA has been duplicated and is condensed and packaged into chromosomes, the nuclear envelope begins to break down and the mitotic spindle forms at opposite ends of the cell. The spindle, which is made of microtubules, is the structure that is required to separate the chromosomes and pull them into two distinct sets.
Credit: Benedict Campbell, Wellcome Images.
Illustration of a cell at prometaphase
Illustration of a cell at prometaphase
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Computer-generated illustration showing a cell at the intermediate stage of prometaphase, which follows prophase. The newly formed chromosomes move towards the centre of the cell to attach themselves to the spindle.
Credit: Benedict Campbell, Wellcome Images.
Illustration of a cell at metaphase
Illustration of a cell at metaphase
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Computer-generated illustration of a cell at metaphase. This stage follows prometaphase and indicates completion of chromosome alignment. During metaphase, the chromosomes are attached to the mitotic spindle via protein complexes called kinetochores. The chromosomes (which consist of two chromatids) line up along the central region of the spindle, called the metaphase plate, so that the sister chromatids face opposite poles.
Credit: Benedict Campbell, Wellcome Images.
Illustration of a cell at anaphase
Illustration of a cell at anaphase
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Computer-generated illustration of a cell at anaphase. At this stage, the paired chromatids that make up each chromosome separate and are visible moving to opposite poles of the cell. The next phase, telophase, begins when the chromatids reach the end of the spindle.
Credit: Benedict Campbell, Wellcome Images.
Illustration of a cell at telophase
Illustration of a cell at telophase
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Computer-generated illustration of a cell at telophase. Once the duplicated chromosomes have separated, the nuclear membranes start to form around them and the chromosomes start to unravel. Then, the cell begins to divide and the cytoplasm of the original cell starts to split. This process, known as cytokinesis, is the final step in forming two new identical daughter cells.
Credit: Benedict Campbell, Wellcome Images.
HeLa cell at late prophase
HeLa cell at late prophase
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Fluorescence micrograph showing a HeLa (human cancer) cell at late prophase. During prophase, the DNA starts to compact into chromosomes to make it easier to separate during later stages of mitosis. Chromatin is formed when DNA, histone proteins and other scaffolding proteins come together to ‘package’ up the DNA into chromosomes. The presence of chromatin indicates condensed DNA, and is seen here in red. The microtubules of the mitotic spindle, which also starts to form, is stained here in green.
Credit: Matthew Daniels, Wellcome Images.
HeLa cell at prometaphase
HeLa cell at prometaphase
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Fluorescence micrograph showing a HeLa (human cancer) cell at prometaphase. This is the same cell as shown in the previous image, but it has started to progress to the next stage of mitosis. The chromatin (in which the chromosomes are packaged) is stained red and the microtubules of the spindle are stained green. The chromatin has fully condensed and the spindle is visible and fully formed, but the chromosomes are not yet organised and have not completely attached to the spindle.
Credit: Matthew Daniels, Wellcome Images.
HeLa cell at metaphase
HeLa cell at metaphase
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Fluorescence micrograph showing a HeLa (human cancer) cell at metaphase. At this stage, the chromosomes (each a pair of sister chromatids) have become attached to the mitotic spindle via specialised proteins called kinetochores. The kinetochores attach each chromatid to the end of the spindle opposite its sister chromatid. In this image the microtubules of the spindle are stained green and the kinetochores are shown as discrete red dots on the end of each spindle microtubule. The chromosomes are not stained in this image but are aligned in the dark area across the middle.
Credit: Matthew Daniels, Wellcome Images.
HeLa cell at metaphase
HeLa cell at metaphase
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Wide-field fluorescence micrograph showing a HeLa (human cancer) cell at metaphase. The metaphase plate is clearly seen with the chromosomes aligned along it in the centre. The chromosomes have been stained to mark the DNA and are shown in white. The centromeres (condensed regions of the chromosomes where the two sister chromatids meet) are shown in yellow. The microtubules that make up the spindle are stainedturquoise. A specialised kinase protein known as ‘Aurora B’, which is required for correct formation and disassembly of the spindle during mitosis, is stained purple.
Credit: Paul Andrews, Wellcome Images.
HeLa cell at anaphase
HeLa cell at anaphase
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Fluorescence micrograph showing a HeLa (human cancer) cell at anaphase. The chromatin (in which the chromosomes are packaged) is shown in red, the microtubules that form the spindle in green, and the cytoplasm in blue. The chromosomes are seen clearly separating from each other and moving along the spindle to the opposite poles of the cell.
Credit: Matthew Daniels, Wellcome Images.
Fruit fly cells in anaphase
Fruit fly cells in anaphase
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Fluorescence micrograph showing a number of Drosophila (fruit fly) cells undergoing anaphase. The microtubules of the spindle are stained green, the chromosomes are shown in blue moving along the length of the spindle and are attached by a protein complex (shown as a red dot).
Credit: Dr Jordan Raff, Wellcome Images.
Dividing human cells at telophase
Dividing human cells at telophase
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Fluorescence micrograph showing a dividing human cell during telophase. The protein shown in red is thought to be important in attaching the chromosomes to the spindle. The microtubules that make up the spindle are labelled in green. At this stage the chromosomes are observed clearly separated at the two poles and the cell is ready to complete cell division.
Credit: Dr Jordan Raff, Wellcome Images.
HeLa cells undergoing cytokinesis
HeLa cells undergoing cytokinesis
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Wide-field fluorescence micrograph of HeLa (human cancer) cells undergoing cytokinesis, the final stage of cell division. The chromosomes are visible as a result of staining that makes the DNA red. The microtubules that formed the mitotic spindle are shown in purple, as they begin to break down. The protein required for this disassembly is a kinase called Aurora B and is stained green. The cytoskeleton protein actin is stained white and is involved in forming a contractile ring around the cytoplasm to separate the cell into two new cells.
Credit: Paul Andrews, Wellcome Images.
The mitotic spindle
The mitotic spindle
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The mitotic spindle of a dividing kidney cell has been stained green to show the tubulin, the protein that makes up the microtubules of the spindle. Desmosomal junctions, which are important for cell-cell adhesion and interaction between the cells, are disrupted during cell division and can be seen in red.
Credit: MRC NIMR, Wellcome Images.
The mitotic spindle
The mitotic spindle
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Confocal micrograph showing the structure of the mitotic spindle. During cell division, specialised structures are formed in the cells to separate the DNA, including the mitotic spindle. During cell division the DNA duplicates and condenses into duplicate chromatids that are pulled to opposite poles by the spindle. Once the chromosomes have separated, the cell divides and forms two new identical daughter cells. The spindle is composed of long chains of the protein tubulin, which form microtubules.
Credit: Dr B Strauss, Wellcome Images.
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