Question

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.

Answer 1

The centromere is a constriction present on the chromosomes where the chromatids are held together.

Chromosomes are divided into four types based on the position of the centromere.

(i) Metacentric chromosome

The chromosomes in which the centromere is present in the middle and divides the chromosome into two equal arms is known as a metacentric chromosome. During anaphase, they appear V-shaped.

(ii) Sub-metacentric chromosome

The chromosome in which the centromere is slightly away from the middle region is known as a sub-metacentric chromosome. In this, one arm is slightly longer than the other. During anaphase, they appear L-shaped.

(iii) Acrocentric chromosome

The chromosome in which the centromere is located close to one of the terminal ends is known as an acrocentric chromosome. In this, one arm is extremely long and the other is extremely short. During anaphase, they appear J-shaped.

(iv) Telocentric chromosome

The chromosome in which the centromere is located at one of the terminal ends is known as a telocentric chromosome. During anaphase, they appear I-shaped.