Dark DNA: Dark matter of Biology
Until the start of 2018, it is believed that DNA has all the information of everything. DNA sequencing technology is helping researchers in finding out the hidden information. By mapping out the whole genome of an organism, we now have a better idea why giraffe has got its long neck and why snakes are so long. Genome sequencing technology allows us to compare and contrast the DNA of different organisms and understand how they evolved and got such unique features. And same thinking applies to the Humans, different skin colors, eye colors, hair, height etc.
But then we come up with a biological dark mystery the “DARK DNA” close to the Dark matter which covers about 25% of the universe, and yet so far remains unsolved mystery. And now biology has same dark mysteries which are still unknown!
Some animal genomes have missing part in their DNA, which is thought to be important for existence. This apparently missing part of DNA/genes have been dubbed “Dark DNA”. And it’s existence could change the way we understand about evolution.
In a recent study published in the journal PNAS, scientists looked at one case involving sand rats (Psammomys obesus), a species of gerbil that lives in deserts of North Africa and Middle East. Scientist, looking for a particular gene called “pdx1” related to the production of insulin, to understand why this animal is particularly susceptible to type 2 diabetes.
But when researchers looked for a gene “Pdx1” responsible for the secretion of Insulin, found out that it was missing with 87 other surrounding genes.
Scientist were stunned, when they find these creatures are living healthy, without these genes including “Pdx1” which are supposed to be essential for survival. So the question is where are they?
They found out that genes weren't really missing but hidden somewhere in the genome. Because they found chemical instructions in desert rat systems, which could only be produced by Pdx1.
The DNA sequences of these genes are rich in G and C molecules which are two of four bases “AGCT” which makes up the DNA. We know that GC rich sequences are problematic for some DNA sequencing technologies. Which makes sense that these genes are not detectable rather than completely missing. Because of that, researchers called this region “missing part” of DNA as a “Dark DNA” with reference to Dark matter which covers about 25% of the universe which scientist have no clue about it.
Digging deeper into the mysterious genome of Sand rat, researcher find out the unexpected number of mutations, far more than the other closely related species. GC content is much higher in the mutated region, making hard to detect for standard methodologies. Excessive mutation can often stop gene from its working. But sand rat’s gene somehow manage to fulfill this gap despite of radical change in the DNA.
“Dark DNA” is rare but not so new, it was previously discovered in bird species’s DNA. In a study published in Genome biology, researchers found 274 missing genes in many bird species, yet necessary for almost all vertebrates. Once again, GC rich DNA was detected, products of which are found in some body tissues, even though genes were apparently missing.
Adam Hargreaves is a Postdoctoral Research Fellow at Oxford, who took part in this study. He and his colleagues called these space where gene are appeared to be missing as “Hotspots”.
Hargreaves and colleagues believe the desert rat may have undergone a fast evolutionary jump, which is why the hotspot occurred. Today, human driven climate change is speeding up evolutionary processes among many species. More cases of dark DNA could be one result.
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