The gene is the basic functional unit of heredity passed on from parents to children. They are a small section of the DNA double helix and contain information that determine your individual characteristics- your appearance, growth, development, and behaviour are all largely determined by your genes.
According to the human genome project, a human cell has roughly around 30,000 genes. These genes are of different sizes; some have about a few hundred DNA bases whereas others have around 2 million DNA bases.
Most genes code for specific proteins which have specific functions in the body. Every gene has two copies, each copy inherited from a parent.
Our genes can also interact with the external environment and change its function accordingly. Not only do the genes determine our traits but they may also determine our risk of developing certain diseases (genetic disorders) like cystic fibrosis and sickle cell anaemia.