I was at a very interesting seminar and an interesting conversation afterwards.
When the Human Genome Project was completed everyone was surprised at how few gene there were. Only about 20-25,000 protein coding genes. It was not that much larger than that for much simpler organisms. So where was the greater complexity of humans and other mammals coming from? Where was the coding for the difference between human brains and those of other mammals?
People speculated that more complex organisms had much more complex regulatory systems in their genomes. Also splicing of different transcribed nucleic acid sequences together allows for an expanded proteome (suite of available proteins) from a genome that has not increased in size. The speculation is tha evolution mostly acts by affecting non-coding rather than coding DNA.
Now part of the regulatory apparatus is what are call micro-RNAs. These are short RNA sequences about 20-23 base pairs long. It was thought that there were several hundred and then thought that there were several thousand micro-RNAs in the cells of a given mammalian species.
The talk I went to today was on estimating how many micro-RNAs there were in a given species. It turned out to be a lot. An awful lot. In a mouse they estimated that there were over a million micro-RNAs. Less complicated organisms had an order of magnitude or more less micro-RNAs. And what was really interesting was that humans had over three million different micro-RNAs. Nothing else came close.
Guess what they think most of the extra micro-RNAs in humans are doing? That's right. They are probably a major part of the plan of the brain.
We have known the genetic alphabet for about fifty years. This is finding that there was a whole chunk of the dictionary that was much bigger and more important than we thought it was.