INTRODUCTION

A eukaryotic cell typically has a great deal of genetic material. For example, if the DNA of a human cell were uncoiled and lined end-to-end, it would extend approximately two meters! This genetic material is replicated before cell division and then must be divided equally between daughter cells. In mitosis, which is the division of the nucleus, the chromosomes condense into bodies small enough to travel efficiently in the cell, and then the chromosomes play out an intricate choreography. At the end of mitosis, the chromosomes have been partitioned into two new nuclei. These nuclei become part of daughter cells that are genetically identical to each other and to the parent cell.

The accompanying animation depicts the movements of chromosomes in mitosis, the dissolution and reformation of nuclear membranes, the formation of the mitotic spindle, and the division of the cytoplasm (called cytokinesis) that results in two new daughter cells.

Video titled: Animation 7.1 Mitosis

Transcript Area

CONCLUSION

Although mitosis is a continuous event, biologists typically divide it into a series of phases. The phases of mitosis are the following:

· In prophase, the chromatin condenses, causing the chromosomes to shorten. The nucleolus also breaks down and the centrosomes move apart and begin to build the mitotic spindle.

· In prometaphase, the nuclear membrane breaks down, allowing the spindle to invade the nuclear region. The spindle fibers capture the condensing chromosomes by the kinetochores found at their centromeres.

· In metaphase, the spindle fibers pull the chromosomes to the equatorial plate.

· In anaphase, the spindle fibers shorten and the opposite poles of the cell move apart. These processes pull the chromosomes apart, such that each chromatid of a chromosome is dragged to the opposite pole of the cell.

· In telophase, the spindle breaks down. The chromatin also begins to uncoil, causing the chromosomes to elongate. Nuclear membranes form around the decondensing chromosomes, and nucleoli again appear.

Cytokinesis, the division of the cytoplasm, follows mitosis. In this part of the cell division cycle, a contractile ring pinches the cell at its midplane. The two daughter cells that form are each genetically identical to the parent cell.

Textbook Reference: Key Concept 7.2 Asexual Reproduction Results in Genetically Identical Daughter Cells, p.154

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