What is a genome?

Our bodies are made up of millions of cells (100,000,000,000,000), each with their own complete set of instructions for making us, like a recipe book for the body. This set of instructions is known as our genome and is made up of DNA. Each cell in the body, for example, a skin cell or a liver cell, contains this same set of instructions:

• The instructions in our genome are made up of DNA.
• Within DNA is a unique chemical code that guides our growth, development and health.
• This code is determined by the order of the four nucleotide bases that make up DNA, adenine, cytosine, guanine and thymine, A, C, G and T for short.
• DNA has a twisted structure in the shape of a double helix.
• Single strands of DNA are coiled up into structures called chromosomes.
• Your chromosomes are located in the nucleus within each cell.
• Within our chromosomes, sections of DNA are “read” together to form genes.
• Genes control different characteristics such as eye colour and height.
• All living things have a unique genome.
• The human genome is made of 3.2 billion bases of DNA but other organisms have different genome sizes.

If printed out the 3.2 billion letters in your genome would:

• Fill a stack of paperback books 200 feet (61 m) high
• Fill 200 500-page telephone directories
• Take a century to recite, if we recited at one letter per second for 24 hours a day
• Extend 3,000 km (1,864 miles), that’s about the distance from London to the Canary Islands, Washington to Guatemala or from New Delhi to Hanoi.

If printed out 1 mm apart, the DNA letters in your genome would extend 3,000 km.