What is a centromere? How does the position of centromere form the basis of classification of chromosomes. Support your answer with a diagram showing the position of centromere on different types of chromosomes.

• The centromere is a specialized constricted region of a chromosome that plays a critical role during cell division.

• It is the site where sister chromatids (the identical halves of a replicated chromosome) are joined together.

• During mitosis and meiosis, the centromere is the attachment point for spindle fibers via the kinetochore, ensuring proper segregation of chromosomes to daughter cells.

Classification of Chromosomes Based on Position of Centromere

The position of the centromere divides the chromosome into two arms—short arm (p arm) and long arm (q arm). Based on the relative lengths of these arms, chromosomes are classified into four types:

• Metacentric chromosome

  • The centromere is located in the center.

  • Both arms are of equal length.

  • Shape: V-shaped during anaphase.

• Submetacentric chromosome

  • The centromere is slightly off-center.

  • One arm is slightly longer than the other.

  • Shape: L-shaped during anaphase.

• Acrocentric chromosome

  • The centromere is close to one end.

  • One arm is much longer than the other.

  • Shape: J-shaped during anaphase.

• Telocentric chromosome

  • The centromere is at the terminal end.

  • Effectively only one arm is visible.

  • Shape: Rod-shaped.

  • Note: Telocentric chromosomes are not found in humans but may be present in some other organisms (e.g., mice).