![]() In plants a cell plate forms along the line of the metaphase plate in animals there is a constriction of the cytoplasm. The final cellular division to form two new cells. The nuclear membrane reforms around the chromosomes grouped at either pole of the cell, the chromosomes uncoil and become diffuse, and the spindle fibres disappear. The final stage of mitosis, and a reversal of many of the processes observed during prophase. (It is the alignment and separation in metaphase and anaphase that is important in ensuring that each daughter cell receives a copy of every chromosome.) The separated sister chromatids are now referred to as daughter chromosomes. The centromeres divide, and the sister chromatids of each chromosome are pulled apart - or 'disjoin' - and move to the opposite ends of the cell, pulled by spindle fibres attached to the kinetochore regions. The chromosomes align themselves along the metaphase plate of the spindle apparatus. ![]() Individual spindle fibres bind to a kinetochore structure on each side of the centromere. The spindle fibres bind to a structure associated with the centromere of each chromosome called a kinetochore. This region of the mitotic spindle is known as the metaphase plate. The chromosomes, led by their centromeres, migrate to the equatorial plane in the mid-line of the cell - at right-angles to the axis formed by the centrosomes. Each replicated chromosome can now be seen to consist of two identical chromatids (or sister chromatids) held together by a structure known as the centromere. The chromosomes condense into compact structures. The centrosomes organise the production of microtubules that form the spindle fibres that constitute the mitotic spindle. A structure known as the centrosome duplicates itself to form two daughter centrosomes that migrate to opposite ends of the cell. The nuclear membrane breaks down to form a number of small vesicles and the nucleolus disintegrates. Mitosis, although a continuous process, is conventionally divided into five stages: prophase, prometaphase, metaphase, anaphase and telophase. In the adult organism, mitosis plays a role in cell replacement, wound healing and tumour formation. Mitotic divisions of the zygote and daughter cells are then responsible for the subsequent growth and development of the organism. In diploid multicellular organisms sexual reproduction involves the fusion of two haploid gametes to produce a diploid zygote. In some single-celled organisms mitosis forms the basis of asexual reproduction. This separation of the genetic material in a mitotic nuclear division (or karyokinesis) is followed by a separation of the cell cytoplasm in a cellular division (or cytokinesis) to produce two daughter cells. The replicated chromosomes are attached to a 'mitotic apparatus' that aligns them and then separates the sister chromatids to produce an even partitioning of the genetic material. In actively dividing animal cells, the whole process takes about one hour. Chromosomes replicated during the S phase are divided in such a way as to ensure that each daughter cell receives a copy of every chromosome. Mitosis is a form of eukaryotic cell division that produces two daughter cells with the same genetic component as the parent cell. ![]()
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