Explanation

I. The shortening and thickening of chromosome fibres occurs due to the two reason Coming together of axial proteins and coiling or spiralisation of chromatin fibres. This is assisted by the proteins, called condensins II. Sometimes, overlapping is shown by the elongated chromosome. Their ends are not visible. Therefore, the chromosomes appears like a ball of wool and this stage is called sprime stage III. Animal cells generally have two centrosome or centriole pairs lying close together. These two centrides begins to move towards the opposite sides of the microtubules, surrounding each pair of centrioles (diplosome). It look like a star-shaped body called aster IV. Shortening of chromosome during prophase is must for their equal distribution during anaphase. Each chromosome appears to have two longitudinal threads called chromatids or sister chromatids, attached to each other by means of a narrow point called centromere