Q.14:- 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.
Centromere is a narrow non-stainable area, which join two similar threads or chromatids of a late prophase or metaphase chromosome. The two parts of the chromosome on either side of the centromere are known as arm. They may be isobranchial (equal) or helerobranchial (unequal in length). Depending upon the position of the centromere, the chromosomes are classified as:
→ Acrocentric chromosome: Centromere sub-terminal, anaphasic stage J-shaped.
→ Sub-metacentric chromosome: The centromere is sub-median and the anaphasic chromosome appear L-shaped.
→ Metacentric chromosomes: The centromere is in the middle and the chromosome appears V-shaped.
→ Telocentric chromosome: Centromere is terminal, anaphasic stage is I-shaped.
Depending upon the number of centromeres a chromosome possess, it may be monocentric, dicentric (two centromeres), polycentric (many centromeres), acentric chromosome (having no centromere).