Junk DNA: A Journey Through the Dark Matter of the Genome by Nessa Carey Page A

humans really don’t need an appendix – this seems like taking imperfection rather too far.
    A much more likely scenario in our car factory would be that for every two people assembling a car, there are 98 others doing all the things that keep a business moving. Raising finance, keeping accounts, publicising the product, processing the pensions, cleaning the toilets, selling the cars etc. This is probably a much better model for the role of junk in our genome. We can think of proteins as the final end points required for life, but they will never be properly produced and coordinated without the junk. Two people can build a car, but they can’t maintain a company selling it, and certainly can’t turn it into a powerful and financially successful brand. Similarly, there’s no point having 98 people mopping the floors and staffing the showrooms if there’s nothing to sell. The whole organisation only works when all the components are in place. And so it is with our genomes.
    The other shock from the sequencing of the human genome was the realisation that the extraordinary complexities of human anatomy, physiology, intelligence and behaviour cannot be explained by referring to the classical model of genes. In terms of numbers of genes that code for proteins, humans contain pretty much the same quantity (around 20,000) as simple microscopic worms. Even more remarkably, most of the genes in the worms have directly equivalent genes in humans.
    As researchers deepened their analyses of what differentiates humans from other organisms at the DNA level, it became apparent that genes could not provide the explanation. In fact, only one genetic factor generally scaled with complexity. The only genomic features that increased in number as animals became more complicated were the regions of junk DNA. The more sophisticated an organism, the higher the percentage of junk DNA it contains. Only now are scientists really exploring the controversial idea that junk DNA may hold the key to evolutionary complexity.
    In some ways, the question raised by these data is pretty obvious. If junk DNA is so important, what is it actually doing? What is its role in a cell, if it isn’t coding for proteins? It’s becoming apparent that junk DNA actually has a multiplicity of different functions, perhaps unsurprisingly given how much of it there is.
    Some of it forms specific structures in the chromosomes, the enormous molecules into which our DNA is packaged. This junk prevents our DNA from unravelling and becoming damaged. As we age, these regions decrease in size, finally declining below a critical minimum. After that, our genetic material becomes susceptible to potentially catastrophic rearrangements that can lead to cell death or cancers. Other structural regions of junk DNA act as anchor points when chromosomes are shared equally between different daughter cells during cell division. (The term ‘daughter cell’ means any cell created by division of a parental cell. It doesn’t imply that the cell is female.) Yet others act asinsulation regions, restricting gene expression to specific regions of chromosomes.
    But a great deal of our junk DNA is not simply structural. It doesn’t code for proteins, but it does code for a different type of molecule, called RNA. A large class of this junk DNA forms factories in the cell, helping to produce proteins. Other types of RNA molecules transport the raw material for protein production to the factory sites.
    Other regions of junk DNA are genetic interlopers, derived from the genomes of viruses and other microorganisms that have integrated into human chromosomes, like genetic sleeper agents. These remnants of long-dead organisms carry potential dangers to the cell, the individual and sometimes even to wider populations. Mammalian cells have developed multiple mechanisms to keep these viral elements silent, but these systems can break down. When they do, the effects can range from relatively benign –