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

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.

(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.

(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.

(iv) Telocentric chromosome
 The chromosome in which the centromere is located at one of the terminal ends is known as a telocentric chromosome.