Chromosomes

Chromosomes are rod-shaped structures that contain genes, which are the hereditary units. They are made up of chromatin material and appear during cell division. Chromosomes consist of two parts - arms and centromere - and are composed of DNA and histone proteins. At the start of cell division, each chromosome has two identical thread-like structures called chromatids or sister chromatids.

Types of Chromosomes

Chromosomes types based on centromere position are:

(i) Metacentric: equal arms

(ii) Sub-metacentric: unequal arms

(iii) Acrocentric/sub-telocentric: one small and one long arm, subterminal centromere

(iv) Telocentric: centromere at chromosome end.

Formation of Chromosomes

Eukaryotic chromosomes are made of chromatin fiber, consisting of nucleosomes and packaged by proteins. Chromatin allows DNA to fit into the nucleus. During cell division, chromatin condenses into visible chromosomes. Chromosome structure varies in the cell cycle and plays a role in genetic diversity and the survival of progeny.