The genome is the complete set of genes or genetic material present in a cell or organism. The human genome is made up of 20,000 genes and more than 3 billion base pairs of the genetic letters known as DNA building blocks (A, T, C, Gs). A genome sequence is a specific order of those DNA building blocks (A, T, C, Gs) and ‘sequencing’ is a critical first step to understanding it and figuring out the order of those DNA nucleotides, or bases, in a genome—that make up who you are.