The Stages of Mitosis Interphase • the chromatin thickens into chromosomes • the chromosomes duplicate (during S phase), but remain intertwined together, enclosed within the nucleus • each chromosome consists of 2 sister chromatids joined to one another at the centromere • in cells of animals and primitive plants, there is a pair of centrioles located in the cytoplasm just outside the nucleus Prophase (the stage before) • appearance of the nucleus changes-beginning of mitosis • chromosomes coil and thicken, becoming visible under light microscope • nuclear envelope disintegrates • the spindle apparatus attaches to the chromosomes at the centromeres • centrosomes move away from each other toward opposite ends (poles) of the cell • microtubules create a spindle, actually 2 half spindles, looks like a football, with chromosomes in the middle, microtubules extending from one pole to the other, some radiate outwards forming a star-shaped • aster forms around the centriole (in animal cells only) • prophase stage is over when nuclear envelope has disappeared entirely, spindle is completely formed, all chromosomes are attached to spindle microtubules Metaphase (the middle stage) • the spindle is fully formed • the spindle fibers align the chromosomes along the equator of the cell • sister chromatids of each chromosome face opposite poles of the cell • spindle fibers connect each chromosome at its centromere to the appropriate end of the spindle Anaphase • sister chromatids separate at the centromere into two independent chromosomes • chromosomes move toward opposite ends of the cell • one sister chromatid of each pair moves toward each pole • sisters are identical copies of original chromosomes • each pole has identical clusters of chromosomes, copies of all originals Telophase (the end stage) • one complete set of chromosomes reaches each pole of the spindle • spindle disintegrates, • nuclear envelope begins to form around each group of chromosomes • chromosomes become thin and extended, can no longer see them • usually cytokinesis happens at this time Cytokinesis • cell membrane pinches cytoplasm in half • in plant cells - new cell wall forms on cell plate for 2 new cells • in animal cells, cell membrane cleaves, indents until 2 form *****Two New Daughter cells result***** result =two nuclei that are identical to each other and to the parent---> clones a single cell can give rise to a vast number of others. This could be for growth or repair or asexual reproduction. It could be an entire organism reproducing or a single cell that divides to produce a multicellular organism. Reproduction by mitosis is very common in nature- aka asexual or vegetative reproduction. Mitosis produces genetically identical offspring.
