User:Puja rani10/sandbox

(Gk. meta-after or second, phasis-appearance or stage). It is the stage of karyokinesis where the replicated chromosomes are brought in equilibrium position for the equitable distribution of their daughters. For this they come to lie over the equator of the spindle. Each chromosome has two chromatids which are attached to each other in the region of their centromeric portions. Each chromosome is connected to both the spindle poles by separate chromosomes fibres in the region of its centromere. On the equator, smaller chromosomes occur in the interior while the larger chromosomes occur on the periphery. Centromeres of all the chromosomes lie over the equator to form an apparent plate called metaphasic or equatorial plate. The limbs of the chromosomes lie in various directions. Spindle apparatus appears over the region of nucleoplasm after the degeneration of nuclear envelope. It is bipolar, amphiaster in animal cells and anastral in plant cells. The apparatus contains microtubular fibres of two types-continuous (interpolar) and discontinuous (incomplete). Chromosomes occur in bivalents having chiasmata. The two chromosomes of a bivalents gets attached to different discontinuous fibres belonging to different poles in the region of their centromeric complexes. The arrangement is random so that any of the paternal or maternal chromosomes can get connected to any of the spindle pole. They contract and and bring the bivalents over the equator of the spindle. This phenomenon is called congression.

'''Metaphase is the best stage to count the number of chromosomes and study their morphology. '''