Hank Green: It's often the case that the least interesting stuff about science is the most discussed in general science media, take, for example, the case of the glow in the dark rat.  Genetic engineering is fascinating and powerful and holds potential to lower the cost of food, save millions of lives, cure previously incurable diseases, and yes, make rats that can glow green under UV light.  For some reason, that latter fact more than any of the former has been far more interesting to the major news media, why?  Because pics or it didn't happen.

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Seriously, though, that's why.  It's why everyone in the world knows that scientists can make rats glow under UV light while very few people know that scientists have made rats that are genetically modified to exhibit symptoms of Alzheimer's allowing scientists to test treatments for debilitating diseases more quickly and effectively.  But they don't glow, so meh.  And yes, we at SciShow have been known to throw in a glowing rat reference here and there, so we can make a nice clickable thumbnail out of the deal, but what's really rarely discussed is why.  Why glowing rats, what's the point?  Are they just a bunch of Dr. Frankensteins throwing jellyfish DNA into various animals to see if they grow, are they practicing their evil laugh while they do it?  

Well, first, these animals don't actually glow in the dark, they fluoresce under UV lights, so already they're a little bit less mad scientist-y and a little more disappointing.  But aside from being really fun at a rave, what use might a rat glowing under UV light be for a geneticist?  Well, it turns out when you're genetically engineering an organism, you often aren't sure if the DNA you intended to insert actually got inserted.  Maybe your gene gun misfired, or maybe the virus you were using to insert the DNA was killed off by the animal's immune system too quickly.  And if you're inserting a gene that might say, decrease a rat's chance of getting certain kinds of cancer, there's no real easy way to see if the DNA got into the rat.  So, I guess, you could take the rat's DNA out and sequence the entire genome to see if the sequence you meant to get in got inserted, or you could tie the gene you want inserted to another gene.  A gene that produces, say, a protein that fluoresces under UV light.  Then, if you want to see if you've successfully added the gene of interest to the rat, all you have to do is bust out the black light.  Really, it's a genius solution to a complicated problem, but mostly we in the scientific communications business just get all excited about the glowing, because apparently, we're as easily distracted as five year olds.  

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