用英语描述细胞有丝分裂和减数分裂的过程、意义!

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The process of mitosis is plex and highly regulated.The sequence of events is divided into phases,corresponding to the pletion of one set of activities and the start of the next.These stages are interphase,prophase,prometaphase,metaphase,anaphase and telophase.
The mitotic phase is a relatively short period of the cell cycle.It alternates with the much longer interphase,where the cell prepares itself for cell division.Interphase is therefore not part of mitosis.
Prophase:The two round objects above the nucleus are the centrosomes.The chromatin has condensed.Prometaphase:The nuclear membrane has degraded,and microtubules have invaded the nuclear space.These microtubules can attach to kinetochores or they can interact with opposing microtubules.
Metaphase:The chromosomes have aligned at the metaphase plate.
Early anaphase:The kinetochore microtubules shorten.
Telophase:The decondensing chromosomes are surrounded by nuclear membranes.Cytokinesis has already begun; the pinched area is known as the cleavage furrow.
Mitosis is important for the maintenance of the chromosomal set; each cell formed receives chromosomes that are alike in position and equal in number to the chromosomes of the parent cell.Transcription is generally believed to cease during mitosis,but epigenetic mechanisms such as bookmarking function during this stage of the cell cycle to ensure that the memory of which genes were active prior to entry into mitosis are transmitted to the daughter cells.
Meiosis is a special type of cell division necessary for sexual reproduction.In animals,meiosis produces gametes like sperm and egg cells,while in other organisms like fungi it generates spores.In many organisms,including humans,meiosis begins with one cell containing two copies of each .
Interphase:Before a dividing cell enters meiosis,it undergoes a period of growth called interphase.
* G1 phase:The period prior to the synthesis of DNA.In this phase,the cell increases in mass in preparation for cell division.Note that the G in G1 represents gap and the 1 represents first,so the G1 phase is the first gap phase.
* S phase:The period during which DNA is synthesized.In most cells,there is a narrow window of time during which DNA is synthesized.Note that the S represents synthesis.
* G2 phase:The period after DNA synthesis has occurred but prior to the start of prophase.The cell synthesizes proteins a