A gene is a unit of heredity that is transferred from parents to offspring and is responsible for determining certain characteristics of the offspring. Genes are composed of DNA (deoxyribonucleic acid), which is a long, double-stranded molecule that contains the genetic instructions for the development and function of all living organisms.

Function of Genes:

The function of genes is to encode the information necessary to produce proteins, which are the building blocks of cells and tissues. Proteins play a variety of roles in the body, including:

- Structural support
- Enzymatic catalysis
- Transport of molecules across cell membranes
- Cell signaling and communication
- Immune responses

Chemical Composition of Genes:

Genes are composed of nucleotides, which are the building blocks of DNA. Each nucleotide consists of a sugar molecule (deoxyribose), a phosphate group, and a nitrogenous base. There are four different nitrogenous bases in DNA:

- Adenine (A)
- Thymine (T)
- Guanine (G)
- Cytosine (C)

These bases pair up with each other in a specific way: A always pairs with T, and G always pairs with C. The sequence of these base pairs determines the genetic code that is carried by a particular gene.

In summary, genes are the fundamental units of heredity that are responsible for encoding the information necessary to produce proteins. They are composed of DNA, which is a long, double-stranded molecule that contains the genetic code in the sequence of its base pairs.