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| the division of the cytoplasm |
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| the period of growth followed by nuclear division and cytokinesis |
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| the nuclear division part of the cell cycle |
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| produces daughter nuclei that are different in that they have one half the number of chromosomes the parental nucleus had. |
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| the nuclear units of genetic information divided and distributed by mitotic cell division. |
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| Most eukaryotes have two copies of each type of chromosome in their nuclei, so their chromosome complement is said to be |
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| The two chromosomes of each pair in a diploid cell are called homologous chromosomes—they have the same genes, in the same order in the DNA of the chromosomes. |
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| Other eukaryotes, mostly microorganisms, have only one copy of each type of chromosome in their nuclei, so their chromosome complement is said to be haploid, or n. For example, the orange bread mold Neurospora crassa is haploid |
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| The number of chromosome sets is called the ploidy of a cell or species. |
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| Before a cell divides in mitosis, duplication of each chromosome produces two identical copies of each chromosome called sister chromatids. |
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| As a result of this precise division, each daughter nucleus receives exactly the same number and types of chromosomes, and contains the same genetic information, as the parent cell that entered the division. Th e equal distribution of daughter chromosomes into each of the two daughter cells that result from cell division is called chromosome segregation. |
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| rst and longest stage is interphase (Figure 10.3). Three phases of the cell cycle comprise interphase: 1) G1 phase, in which the cell grows; 2) S phase, in which DNA replicates and chromosomal proteins are duplicated; and3) G2 phase, in which cell growth continues and the cell prepares for mitosis (the fourth phase of the cell cycle; also called M phase) and cytokinesis. |
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| G1 is also the stage in which many cell types stop dividing. Cells in a state of division arrest enter a shunt from G1 called the G0 phase. |
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| prophase, prometaphase, metaphase, anaphase, telophase |
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| the greatly extended chromosomes that were replicated during interphase begin to condense into compact, rodlike structures |
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| In the cytoplasm, the mitotic spindle (Figure 10.6; see also Figure 10.11), the structure that actually separates chromatids, begins to form between the two centrosomes as they start migrating toward the opposite ends of the cell, where they will form the spindle poles. |
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| At the end of prophase, the nuclear envelope breaks down, heralding the beginning of prometaphase. Bundles of spindle microtubules grow from centrosomes at the opposite spindle poles toward the center of the cell. Some of the developing spindle enters the former nuclear area. Each chromosome is still a double structure made up of two identical sister chromatids held together only at their centromeres. By this time, a complex of several proteins, a kinetochore has formed on each chromatid at the centromere, a region located at a particular position in a given chromosome. |
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| , the spindle reaches its final form and the spindle microtubules move the chromosomes into alignment at the spindle midpoint, also called the metaphase plate. Th e chromosomes complete their condensation in this stage. Th e pattern of condensation gives each chromosome a characteristic shape, determined by the location of the centromere and the length and thickness of the chromatid arms. |
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| The complete set of metaphase chromosomes, arranged according to size and shape, forms the karyotype of a given species. |
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| girdles the cell and gradually deepens until it cuts the cytoplasm into two parts. |
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| In plants, a new cell wall, called the cell plate, forms between the daughter nuclei and grows laterally until it divides the cytoplasm in two |
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| During anaphase, the spindle separates sister chromatids and pulls them to opposite spindle poles. Th e fi rst signs of chromosome movement can be seen at the centromeres where tension developed by the spindle pulls the kinetochore toward opposite poles. Th e movement continues until the separate chromatids, now called daughter chromosomes, hav reached the two poles. At this point, chromosome segregation has been completed |
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| During telophase, the spindle disassembles and the chromosomes at each spindle pole decondense, returning to the extended state typical of interphase. As decondensation proceeds, the nucleolus reappears, RNA transcription resumes, and a new nuclear envelope forms around the chromosomes at each pole producing the two daughter nuclei. At this point, nuclear division is complete, and the cell has two nuclei. |
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| Vegetative or asexual reproduction |
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| Mitosis also serves as a method of reproduction called vegetative or asexual reproduction, which occurs in many kinds of plants and protists and in some animals. |
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| centrosome, a site near the nucleus from which microtubules radiate outward in all directions, and its role in spindle formation. Th e centrosome is the main microtubule organizing center (MTOC) of animal cells and many protists. Th e centrosome contains a pair of centrioles, usually arranged at right angles to each other. Although centrioles originally appeared to be important in the construction of the mitotic spindle, they can be removed experimentally with no ill eff ect. |
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| the centrosomes at the cpindle tips, which form the poles of the spindle |
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