Genomes: not just genes

Making molecules

Genes were once defined as lengths of DNA that carried the instructions to make a protein. Researchers now know that the instructions in some genes can produce many proteins, and that other genes are transcribed into RNA, but don't ever produce a protein.

No-one is sure exactly how many genes there are in the human genome, but the latest estimate suggests between 20,000-25,000 - barely a third more than a fruit fly! During the Human Genome Project, researchers placed bets on the number of human genes. Their estimates ranged from 27,462 to 200,000 ...

Although genes make up about a third of our genome, only about 2% of the DNA sequence is transcribed and translated into protein. At the moment, only about 400 non-protein-coding genes have been found, but the number may be far higher - perhaps thousands.