What Are Genes?
Every living thing — from a tiny bacterium to a blue whale — carries a set of instructions that determines how it grows, develops, and functions. These instructions are called genes.
A gene is a section of DNA that carries the instructions for making a specific protein, which in turn influences a particular characteristic (trait) of an organism.
Think of genes like individual recipes in a giant cookbook. Each recipe (gene) gives instructions for one specific dish (characteristic), and together all the recipes make up the full menu of who you are.
Humans have approximately 20,000–25,000 genes in total, and every cell in your body (with a few exceptions, such as red blood cells which have no nucleus) contains a complete copy of all of them.
DNA: The Molecule of Inheritance
Genes are made of a chemical called DNA (deoxyribonucleic acid). DNA is a long, twisted ladder-shaped molecule — scientists describe its shape as a double helix.
DNA is the molecule that stores genetic information in living organisms. It is made up of four chemical bases — adenine (A), thymine (T), cytosine (C), and guanine (G) — arranged in a specific sequence that acts as a code.
The sequence of these bases is what makes one gene different from another. Just like letters in the alphabet can be arranged to make millions of different words and sentences, the four DNA bases can be arranged to carry an enormous variety of genetic instructions.
Imagine DNA as a very long piece of coded text. The four bases (A, T, C, G) are like the four letters of a very simple alphabet. Different combinations of these letters spell out different instructions — some might say "make blood type A," others say "make free earlobes." (Note: most characteristics are actually controlled by many genes working together, not just one!)
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