Chromosome Structure

Chromosomes are classified by the position of the centromere, the constricted region to which spindle fibres attach during cell division. When the centromere occupies the middle of the chromosome it produces two arms of roughly equal length, and during anaphase such a chromosome bends into a characteristic V-shape; this is the metacentric type defined in NCERT Class 11, Chapter 8 (Cell: The Unit of Life). The acrocentric option is incorrect because there the centromere lies very near one end, producing one extremely short arm and one very long arm, giving a J-shape. The telocentric type, with a strictly terminal centromere giving an i-shape, is also wrong for a chromosome described as having two equal arms. The submetacentric choice is incorrect because its centromere is slightly away from the centre, yielding arms of clearly unequal length and an L-shape. The centromere itself is the primary constriction that bears the kinetochore, the disc-shaped plate where spindle microtubules attach to pull the chromosome poleward. Because the two arms of a metacentric chromosome are of equal mass, both halves are dragged symmetrically, which is exactly what produces its clean V outline during anaphase. A geometric consistency check confirms the answer: only a centromere placed exactly at the midpoint can divide the chromosome into two equal arms and generate the symmetric V-shape observed at anaphase.