What is the human genome?

The human genome is the entire library of genetic information needed to build and maintain a human being, stored as DNA in the nucleus of nearly every cell. It contains about 3 billion base pairs organized into 23 pairs of chromosomes, and surprisingly only around 20,000 genes actually code for proteins — far fewer than scientists once expected. Much of the rest was long called “junk” DNA but is now known to include important regulatory instructions. The Human Genome Project, an international effort, produced the first essentially complete sequence in 2003, and a truly gapless version was announced in 2022.