"Chromosomal material condenses to form compact mitotic chromosomes. Chromosomes are seen to be composed of 2 chromatids attached together at the centromere. " Explain this statement.
Also, what are mitotic spindle and microtubules?
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- Initially chromosomes appear as a long thread in the nucleus. These chromosomes have invisible ends and look like a yarn ball at this stage. Then the chromosomes gradually change into short, thick rods and became visible. This change occurs by condensation (water loss) and spiralisation (chromosome coiling). In the preceding S phase, due to the duplication of chromosomes, each chromosome appears longitudinally double, consisting two identical sister chromatids. These sister chromatids held together at the narrow region called centromere. At this narrow region, each chromatid has the kinetochore (a disc like structure), where the spindle microtubules join it. Chromosomes are fully replicated and double at all points along their length including the centromere.
- Spindle fibres are collectively known as mitotic spindle. Between the separating asters, spindle shaped fibres develops outside the nucleus during mitosis. The fibres that constitute the mitotic spindle, pull the chromatids apart toward opposite poles.
- Microtubules are tiny sub component of the cytoskeleton, found throughout the cytoplasm. Centrioles migrate in pairs to the opposite ends of the cell. Short radiating microtubules assemble around them. These microtubules surrounding each pair of centrioles, look like a start shaped body called aster. They also known as astral rays. They maintain the cell structure and involved in cell division.