Genomes: not just genes
What's in a genome?
The human genome includes all of the genes that code for proteins, together with the control sequences for each gene, and the DNA that occurs between and within genes. The human genome is estimated to be 3,200,000,000 base pairs long.
We actually have two copies of our genome - one from our mother and one from our father - so we manage to pack a lot of DNA into our cells.
Quite simply, we don't know what some our genome does. The bits of DNA we don't understand have often been called 'junk DNA'. However, the more we learn about what's in the 'junk', the more it seems better to call it 'noncoding' DNA' instead.
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.
