Biology · Cell: The Unit of Life · NEET
Only the POSITION of the centromere (the primary constriction) decides the type. The centromere is the point that holds the two chromatids together. Depending on where it sits along the length, the two arms come out equal, unequal, or almost missing. This is important for NEET because questions directly ask you to match centromere position to the chromosome name.
In an ACROCENTRIC chromosome the centromere is very close to one end, so you still see one extremely short arm and one very long arm. In a TELOCENTRIC chromosome the centromere is right at the terminal end (tip), so there is basically only ONE arm and no short arm at all. Simple test: acrocentric = tiny short arm still present; telocentric = short arm gone, centromere at the very end.
Metacentric means the centromere is in the MIDDLE of the chromosome. This splits it into two EQUAL arms, so the chromosome looks like the letter V during anaphase. 'Meta' = middle. This is the shape NEET asks about when the question says 'two equal arms'.
In a submetacentric chromosome the centromere is slightly away from the middle, giving one SHORTER arm and one LONGER arm. The shorter arm is called the p-arm ('p' for petit = small) and the longer arm is called the q-arm. NCERT 2019 asked this exact naming, so remember: p = short, q = long.
When the centromere is pulled during anaphase, the arms drag behind and give a shape: metacentric looks like a V (equal arms), submetacentric looks like an L (unequal arms), acrocentric looks like a J or rod (one tiny arm), and telocentric looks like an i or straight rod (single arm). Matching shape to name is a fast NEET trick.
No. Normal HUMAN chromosomes are only metacentric, submetacentric or acrocentric. Telocentric chromosomes (centromere exactly at the tip) are NOT found in normal humans but are described in the general classification, so NEET can still ask about them theoretically.
The shorter and longer arms of a submetacentric chromosome are referred to as
Spindle fibres attach on to:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Four types: metacentric (middle centromere, equal arms), submetacentric (off-centre, one short one long arm), acrocentric (near one end, very short arm), and telocentric (centromere at the tip, single arm).
The metacentric chromosome. Its centromere lies in the exact middle, so both arms are equal in length and it looks like a V during cell division.
The primary constriction is the centromere. It is the narrow point that holds the two chromatids together, and its position along the chromosome decides whether the chromosome is metacentric, submetacentric, acrocentric or telocentric.
The shorter arm is called the p-arm (from French 'petit' meaning small) and the longer arm is the q-arm. NEET 2019 tested this naming directly.
Not exactly. Spindle fibres attach to the kinetochores, which are disc-shaped structures sitting on the sides of the centromere. The centromere is a common wrong option in NEET.
