Describe the structure of chromosomes with a suitable diagram.

Explanation

1. Structure of chromosomes :
(1) A chromosome during metaphase shows two identical halves. These halves are called sister chromatids.
(2) Each chromajid is made up of sub-chromatids called chromonemata (singular-chromonema).
(3) The chromatids are held together by a centromere or the primary constriction. During cell division the spindle fibres are attached at the centromere. Additional narrow areas called secondary constrictions are seen in some chromosomes which are known as nucleolar organizers. They help in the formation of nucleolus.

(4) The part of the chromosome beyond the nucleolar organizer is called satellite which is short and spherical.
(5) The tip of the chromoson1e is called telomere which helps in preventing the ends of the chromosomes from sticking together. They attach the chromosomes to the nuclear envelope.
(6) The surface of a chromosome bears a number of small swellings called chromomeres.