Explain the structure of chromosomes with suitable diagram.

Explanation

The chromosomes are thin, long and thread like structures, with two identical strands called chromatids. They are held together by centromere. The chromatid is made up of spirally coiled, thin structure called chromonema, which has a number of bead like structure along its length called chromomeres.
A chromosome consists of the following regions:
(a) Primary constriction:
The two arms of a chromosome meet at a point called primary constriction or centromere. The centromere is the region, where spindle fibres attach to the chromosome during cell division.
(b) Secondary constriction:
Some chromosomes have secondary constriction at any point of the chromosome, called the nuclear zone or nucleolar organizer. (Formation of nucleolus in the nucleus).
(c ) Telomere:
The end of the chromosome is called telomere. Each extremity of the chromosome has a polarity and prevents it from joining the adjacent chromosome. It maintains and provides stability to the chromosome.
(d) Satellite:
Some of the chromosomes have an elongated knob-like appendage at one end of the chromosome, known as satellite. The chromosomes with satellites are called as sat-chromosomes.