Q.Draw a neat diagram of metacentric chromosome and label the following :

On a metacentric chromosome, mark the centromere at the exact middle (equal arms), the secondary constriction at a distinct narrow point on one arm (not the centromere), and the satellite as the small knob-like segment beyond the secondary constriction.

(This question asks for a hand-drawn, labelled diagram; since a diagram cannot be physically drawn in this text answer, the structure and correct labelling are described in detail below so it can be reproduced on paper.)

A chromosome, at metaphase, appears as two sister chromatids joined at the centromere, with the DNA-protein fibre organised into two arms extending from the centromere.

• Metacentric type: the centromere lies exactly at the middle of the chromosome, so the two arms on either side are of equal (or nearly equal) length, giving the chromosome a V-shape when the chromatids separate at anaphase.

• (i) Centromere: draw this as the primary, narrow constriction at the exact midpoint of the chromosome, where the two sister chromatids are held together and where spindle fibres attach (via the kinetochore).

• (ii) Satellite: draw a small, rounded, bead-like segment of chromatin attached to the end of one arm, separated from the rest of that arm by the secondary constriction — it appears almost detached, like a small knob at the tip.

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