Genome

An organism's genome is all of its genetic material: every gene, plus the much larger amount of DNA that does not code for protein, such as regulatory regions and repeated sequences. In most organisms the genome is made of DNA, though some viruses carry genomes of RNA. In humans, the nuclear genome is packed into 23 pairs of chromosomes, and mitochondria carry their own small circular genome.

One copy of the human genome is about 3 billion base pairs long and holds roughly 20,000 protein-coding genes, which make up only a small fraction of it. Genome size varies enormously between species and does not track how complex an organism is; some plants have genomes dozens of times larger than ours. Almost every cell in the body carries the same genome, but different cell types use different parts of it.

Reading a genome base by base is called genome sequencing. The Human Genome Project finished the first human reference sequence in 2003, and comparing genomes is now central to medicine, evolution and agriculture. The botanist Hans Winkler coined the German word Genom in 1920.