Changes must be cell division and genetics test pdf before being displayed on this page. The process of mitosis is divided into stages corresponding to the completion of one set of activities and the start of the next. The result is two genetically identical daughter nuclei.
The rest of the cell may then continue to divide by cytokinesis to produce two daughter cells. Most human cells are produced by mitotic cell division. When mitosis begins, the chromosomes condense and become visible. DNA from the cytoplasm, disintegrates into small vesicles. The microtubules then contract to pull the sister chromatids of each chromosome apart.
As the cell elongates, corresponding daughter chromosomes are pulled toward opposite ends of the cell and condense maximally in late anaphase. A new nuclear envelope forms around the separated daughter chromosomes, which decondense to form interphase nuclei. During mitotic progression, typically after the anaphase onset, the cell may undergo cytokinesis. During all three parts of interphase, the cell grows by producing proteins and cytoplasmic organelles. In plant cells only, prophase is preceded by a pre-prophase stage.
This band marks the position where the cell will eventually divide. The preprophase band disappears during nuclear envelope breakdown and spindle formation in prometaphase. In this stage, chromosomes are long, thin and thread-like. Each chromosome has two chromatids. The two chromatids are joined at the centromere. As this happens, microtubules invade the nuclear space. This motor activity, coupled with polymerisation and depolymerisation of microtubules, provides the pulling force necessary to later separate the chromosome’s two chromatids.
After the microtubules have located and attached to the kinetochores in prometaphase, the two centrosomes begin pulling the chromosomes towards opposite ends of the cell. If the cell successfully passes through the metaphase checkpoint, it proceeds to anaphase. Shortening of the kinetochore microtubules pulls the newly formed daughter chromosomes to opposite ends of the cell. In most animal cells, anaphase A precedes anaphase B, but some vertebrate egg cells demonstrate the opposite order of events.
At telophase, the polar microtubules continue to lengthen, elongating the cell even more. If the nuclear envelope has broken down, a new nuclear envelope forms using the membrane vesicles of the parent cell’s old nuclear envelope. Both sets of chromosomes, now surrounded by new nuclear membrane, begin to “relax” or decondense. Each daughter nucleus has an identical set of chromosomes. Cell division may or may not occur at this time depending on the organism. Cytokinesis is not a phase of mitosis but rather a separate process, necessary for completing cell division. Each daughter cell has a complete copy of the genome of its parent cell.
The end of cytokinesis marks the end of the M-phase. There are many cells where mitosis and cytokinesis occur separately, forming single cells with multiple nuclei. The number of cells within an organism increases by mitosis. This is the basis of the development of a multicellular body from a single cell, i. In some parts of body, e. New cells are formed by mitosis and so are exact copies of the cells being replaced.