Have you ever heard that bewildering fact that 25% of the universe is comprised of dark matter? Something that is impossible to see and have no idea what it does. For a long time, genomes were a little like this for geneticists. A genome is the entire sequence of an individual’s DNA, which in humans will stretch out to around 2 metres long fully unravelled. Despite being its namesake, genes (protein-coding) make up a measly 2% of our 2-metre-long DNA.Meanwhile, the other 98% (called non-coding DNA) was once the genome’s dark matter – until recent years scientists had no idea what it was for, or if it even had any purpose at all; they used to call it ‘junk DNA’ but turns out it’s anything but!
Let’s imagine the Ikea warehouse is a genome. Ikea warehouses are known for housing endless boxes of flat pack furniture; the building blocks for your home, that we’ll call ‘the genes’ of this analogy. However, these warehouses also comprise many other parts that we hardly even notice but are equally important. There’s the concrete floor providing support for the whole building, there’s codes and maps to navigate your way around, and there’s all the shelves and tall units to organise the flat pack furniture – some of these are guarded with gated grills to restrict your access. Take those components away and Ikea warehouses would become a mess of disorganisation, they just wouldn’t function!
In a similar way, genes have been the focus point of studying animal genomes but, they’re not even the half of it. Genomes also comprise large stretches of DNA with other hugely important functions; ranging from structural support to regulatory roles like providing information on where to find the gene you’re looking for or which genes should come together, and how for how long one particular gene should be read out for. As genomes are continually being researched, more and more of their components get discovered. That said, many animal genomes’ (including our own) still do contain big, long stretches for which no function has yet been attributed. Perhaps these regions are just ‘junk’– antiques of DNA from the past, that somehow survived through evolutionary culling despite no longer fulfilling any functional purpose. Or alternatively, a bit like your grandma’s garage, it’s not yet entirely obvious what she’s storing all that stuff for, until that one day when something might just come in handy!
