The human genome contains approximately 20,000 protein-coding genes. These genes carry instructions for making proteins, the molecules that perform much of the body’s structural, chemical, and regulatory work.
The estimate changed substantially as genome annotation improved. Before the Human Genome Project, many scientists expected humans to have 50,000, 100,000, or even more genes. Early analyses of the draft genome suggested roughly 30,000 protein-coding genes, but better sequencing and gene-identification methods later reduced the estimate to about 19,000–20,000.
This number does not represent all human genes. The genome also contains genes for non-coding RNAs, pseudogenes, and regulatory elements. Moreover, one protein-coding gene can produce multiple proteins through processes such as alternative splicing. That helps explain why a relatively modest gene count can support the complexity of human biology.