Genome is all 3.2 billion letters of DNA. It contains around 20,000 genes. Genes are the instructions for making the proteins our bodies are built of – from the keratin in hair and fingernails to the antibody proteins that fight infection. Genes make up about 1-5% of your genome. The rest of the DNA, between the genes, used to be called ‘junk’ DNA. It wasn’t thought to be important. But we now know that DNA between genes is important for regulating the genes and the genome. DNA (deoxyribose nucleic acid) is a long molecule. It has a twisted, double helix shape. DNA is made up of four different chemicals, or bases. These are represented by the letters A, T, C and G. The bases are attached to two phosphate backbones. The bases are paired together; A with T, G with C. The two backbones twist around each other to give the characteristic double helix. Sequencing is a technique that is used to ‘read’ DNA. It finds the order of the letters of DNA (A, T, C and G), one by one. Sequencing a human genome means finding the sequence of someone’s unique 3 billion letters of DNA. A genome is an organism’s complete set of genetic information. A genome includes all of the hereditary instructions for creating and maintaining life, as well as instructions for reproduction. The human genome, like all other cellular life forms, consists of DNA and includes both the nuclear and mitochondrial DNA. This is in contrast to ribonucleuic acid (RNA) viruses, whose genome is comprised of RNA.