Q.The stability of chromosome is determined by ________.

Telomeres, the specialised nucleoprotein caps at the two ends of a chromosome, are responsible for chromosome stability.

A typical eukaryotic chromosome has several distinct structural regions, each with a specific role:

• Centromere: the primary constriction where the kinetochore forms; it is the site of spindle-fibre attachment and is essential for chromosome MOVEMENT during cell division, not for the structural integrity of the chromosome ends.
• Satellite: a secondary constriction that marks off a small terminal segment (a 'satellite' body) on some chromosomes — mainly a landmark, not a stability feature.
• Kinetochore: the disc-shaped protein structure built on the centromere that spindle fibres actually attach to; again, a movement/segregation feature. …

The centromere is required for chromosome movement toward the poles during anaphase, because it is the site where spindle-fibre microtubules attach (via the kinetochore) and exert the pulling force.

Go through the options:

1. Transcription — occurs along the length of DNA wherever genes are being expressed; it does not require the centromere specifically.
2. Crossing over — occurs at chiasmata formed between homologous chromosome arms during pachytene of meiotic prophase I; it is unrelated to the centromere.
3. Cytoplasmic cleavage — cytokinesis is driven by the contractile ring (actin-myosin, in animal cells) or cell plate formation (in plant cells); it does not require the centromere. …