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
Chromosome (centromere): In every chromosome there is a primary narrowing which is called chromosome point or centromere. Every chromosome (visible only in dividing cells) essentially has a primary constriction or the centromere on the sides of which disc-shaped structures called kinetochores are present. Based on the position of the centromere, the chromosomes can be classified into four types:
(i) Metacentric: In the chromosome, the centromere is located in the middle of the chromosomes, due to which both the arms of the chromosome are of equal length and they are V-shaped.
(ii) Sub-metacentric: The centromere in the chromosome is away from the middle of the chromosome, as a result of which one arm is shorter and the other arm is longer. The shape of chromosome is J or L shaped.
(iii) Acrocentric: In the chromosome, the centromere is found at its very edge, due to which one arm is very small and the other arm is very long.
(iv) Telocentric: Centromere is located at the top of the chromosome.
Fig.: Types of Chromosomes based on the position of Centromere
(i) Metacentric: In the chromosome, the centromere is located in the middle of the chromosomes, due to which both the arms of the chromosome are of equal length and they are V-shaped.
(ii) Sub-metacentric: The centromere in the chromosome is away from the middle of the chromosome, as a result of which one arm is shorter and the other arm is longer. The shape of chromosome is J or L shaped.
(iii) Acrocentric: In the chromosome, the centromere is found at its very edge, due to which one arm is very small and the other arm is very long.
(iv) Telocentric: Centromere is located at the top of the chromosome.
Fig.: Types of Chromosomes based on the position of Centromere
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