Now: The Rest of the Genome
There are too many exceptions to the rule “one gene to one protein”. The word ‘Gene’ was coined by Danish geneticist Wilhelm Johanssen in 1909. Scientists knew that genes could be turned on or off with proteins attaching to the DNA nearby, some genes coded for RNA molecules which never become proteins. In the 1980s and 1990s scientists found that when a cell produces an RNA transcript large parts of the DNA are cut out, the introns. Only about 1.2% of the genome is protein-coding regions. In 2000 a rough draft of the human genome was made but there was still 99.8% of the genome left unexplored. One big project named Encode (Encyclopedia of DNA Elements) has several hundred scientists doing experiments to discover what each piece of DNA does. So far they published 1% of the genome or roughly three million subunits of DNA. Some of the genes published produce more than one protein in a process called alternative splicing and other genes include exons of other genes into their transcript. The ‘epigenome’ is like a permanent marker they are passed down from generation to generation and keeps a record of what genes are on/off or are never turned on. Encode estimates that 93% of the human genome codes for noncoding RNA which prefrom other jobs. Parts of our DNA are from viruses that invaded human DNA millions of years ago, some are harmful some are useful. For example some virus DNA have evolved to make RNA that our cells use.