What is a genome?

• Organisms are made up of millions of cells (100,000,000,000,000), each with their own complete set of instructions for building and sustaining that living thing.
• This set of instructions is known as our genome and is made up of DNA. Each cell in an organism, for example, a skin cell or a liver cell, contains this same set of instructions.

From genome to genes

• The instructions in our genome are made up of DNA.
• Within DNA is a unique chemical code that guides an organism’s growth, development and health.
• This code is determined by the order of the four nucleotide bases that make up DNA, adenine, thymine, cytosine and guanine.
• DNA has a twisted structure in the shape of a double helix.
• Single strands of DNA are coiled up into structures called chromosomes.
• In animals, chromosomes are located in the nucleus within each cell.
• Within chromosomes, sections of DNA are organised into genes.
• Genes control different characteristics such as eye colour and height.
• All living things have a unique genome.

The human 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 telephone directories, each with 500 pages.
  • 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) – approximately the distance from London to the Canary Islands, Washington to Guatemala, or from New Delhi to Hanoi.