Q.What is the feature of a metacentric chromosome?

If you tied a string around a stick at different points — dead centre, a little off centre, near one end, or right at the tip — you would get four differently balanced shapes. Chromosomes are classified in almost exactly this way, according to where the centromere sits along their length.

Every chromosome, which becomes visible only during cell division, has a primary constriction called the centromere. This is the region that holds the two chromatids of the chromosome together, and on either side of it lie disc-shaped structures called kinetochores. The centromere divides the chromosome into two arms, and the relative lengths of those arms depend entirely on the centromere's position.

Based on that position, chromosomes fall into four types:

• Metacentric — the centromere lies in the middle, so the chromosome has two arms of roughly equal length.
• Sub-metacentric — the centromere is slightly off centre, giving one shorter arm and one longer arm.
• Acrocentric — the centromere lies close to one end, producing one extremely short arm and one very long arm.
• Telocentric — the centromere sits at the very end (terminal position).