genome

A genome is the complete set of genetic instructions for an organism — its entire DNA, taken as a whole. If a single gene is one recipe, the genome is the whole cookbook, from cover to cover, including the index, the blank pages, and the notes in the margins.

The genome includes all of an organism's genes, but it is much more than just the genes. Long stretches between and within genes do not code for proteins, yet they help control when genes turn on, organize the chromosomes, and shape how the DNA is packaged. The genome is the genes plus all of this surrounding sequence.

Most of the human genome is stored on chromosomes in the cell nucleus, with a small, separate genome inside mitochondria. The human nuclear genome is about three billion base pairs long. Nearly every cell in a body carries a complete copy of the genome, even though different cells use different parts of it.

Reading an organism's genome — sequencing it — has become a central tool of modern biology and medicine. But having the sequence is only a first step: much of the work lies in figuring out what the letters mean, which is the domain of genomics and bioinformatics.