Question

Chromosomes are most compacted during which stage of the cell cycle?

a) M phase

b) G2

c) S phase

d) G1

e) At all cell cycle stages

Answer 1

Ans. Correct option- a. M-phase.

As metaphase begins, the phosphorylation of H2A histones by Aurora B and mitotic CDK triggers condensin proteins (SMC family) binding to chromatin. Coupled to topoisomerase II activity, condensin protein forms positively supercoiled and highly condensed chromosome. By the end of metaphase, the chromosomes are in the most condensed form than any other phase of cell cycle.

# Chromosomes are relatively most UN-condensed in G1 phase to facilitate active transcription of genes for normal metabolic and physiological activities of the cell.

# Chromosomes gradually condense as the cell progresses from G1 to M phase.