Q.State one visible structural change undergone by chromatin during prophase of mitosis.

Mitosis is the equational nuclear division in which the daughter cells end up with exactly the same chromosome number as the parent cell, making it responsible for growth, tissue repair and asexual reproduction. In plants it occurs mainly in meristematic tissue (shoot and root tips); it can be closed (spindle forms inside an intact nuclear envelope, as in yeasts and slime moulds) or open (the nuclear envelope breaks down and later re-forms, as in most plants and animals). Mitosis proceeds through four phases. In prophase, chromosomes condense into visible mitotic chromosomes, the nuclear envelope breaks down, and in animal cells the centrioles organise an aster of microtubules at each pole (plant cells, lacking centrioles, do not form asters). In metaphase, chromosomes attach to spindle fibres via their kinetochores and align at the equatorial metaphase plate, checked by the spindle assembly checkpoint. In anaphase, the enzyme complex APC/C degrades cohesin, each centromere splits, and sister chromatids are pulled to opposite poles. In telophase, the spindle disappears, nuclear envelopes re-form around each chromosome set, and cytokinesis completes the physical separation of two genetically identical daughter cells - by a contractile actin-myosin ring in animal cells, or by a phragmoplast-built cell plate in plant cells. Mitosis's significance flows entirely from producing identical copies: genetic stability, growth, tissue repair, asexual reproduction, vegetative propagation, tissue-culture propagation and regeneration all depend on it.