What is a centromere?

What is a centromere? How does the position of the 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 heterobranchial (unequal in length). Depending upon the position of the centromere, the chromosomes are classified as follows
(i) Acrocentric chromosome The centromere is sub-terminal, at anaphasic stage appear J-shaped.
(ii) Sub-metacentric chromosome The centromere is sub-median and the anaphasic chromosome appear L-shaped.
(iii) Metacentric chromosomes The centromere is in the middle and the chromosome appears
V-shaped in anaphase.