Q.2 What are chromosomes and genes. Describe the structure of chromosomes.
Answer:
Genes
Genes consist of DNA. They contain specific instructions for protein synthesis.
Or
Units of inheritance, located on chromosomes are called genes.
Chromosomes
(a) Introduction
Hereditary material found in the nucleus of every cell is called chromosomes.
(b) Constant number
Body cells have a constant number of paired chromosomes.
(c) Homologous chromosomes
The two chromosomes of a pair are known as homologous chromosomes. In human body cells, there are 23 pairs for a total of 46 chromosomes.
(d) Chemical composition :
They are made of chromatin material (chromatin). Chromatin is a complex material, made of DNA and proteins (histone).
(e) Nucleosomes
DNA wraps around histone proteins and forms round structures, called nucleosomes. DNA is also present between nucleosomes.
Beads on a string
The nucleosomes and the DNA between them look like beads on a string.

Chromosomes
The fibers consisting of nucleosomes condenses into compact forms and get the structure of chromosomes.