Beauty comes from junk!

October 24, 2022 6:15 AM

Butterfly wings pattern and junk dna “Reed’s lab has uncovered key color pattern genes: one (WntA) that controls stripes and another (Optix) that controls color and iridescence in butterfly wings.“
posted by Yellow (4 comments total)

Here come the designer butterflies.

Also, this is an entirely new butterfly effect. Not flapping wings in Hong Kong starting a hurricane across the ocean, but, starting with butterflies, deciphering (as the story says) the variable traits of "birds or flies or worms," and then of course everything else.
posted by beagle at 6:45 AM on October 24, 2022 [3 favorites]

Thanks for this heads-up. When I was in grad school 40 years ago, I was in awe of another much more effective population geneticist called John RG Turner who was studying the genetics of wing patterns on Heliconius butterflies . . . with the hottest genetic tools that were available at the time. These wing patterns were at the time billed as the most studied system in the animal kingdom which had no economic value. They were interesting because completely different butterfly species had evolved to resemble each other and to share the burden of training predatory birds to recognise that they were all toxic. It's not much good to an individual butterfly if it is chewed up and spat out (bloooargh) by a bird.
Turner's genetic work is now effectively in the dustbin of history. ResearchGate suggests that the last ten years his scholarship has been devoted to translating the poetry of Verlaine into English! No entry in Wikipedia FWIW.

It's great to see how much detail on the workings of evolution is available with current techniques. I might take issue with the phrase "junk DNA" used in the cited press release from Columbia. There is much more to genomes than the bits which code for proteins. The scientists at Columbia are whacking parts of the DNA which are adjacent to some protein-coding genes to tease apart when and where those genes are 'switched on' to make their protein. If that 'upstream' DNA is not just so, then the gene don't work and the butterfly is likely to have no wing rather one which is merely colored different: I write metaphorically. Other parts of the Heliconius genome are a lot junkier . . . perhaps because we haven't figured out what purpose they serve yet; but also possibly because it is the decaying remnants of long dead viruses and transposable elements.
posted by BobTheScientist at 10:03 AM on October 24, 2022 [3 favorites]

I might take issue with the phrase "junk DNA" used in the cited press release from Columbia.

Indeed; the phrase "junk DNA" could be very misleading, making it sound like we've learned something new about animal genomes, rather than something cool about butterflies and their evolution.

Non-coding DNA is the standard terminology for bits like this that act as regulatory switches; they've been known for a while. Hugely important, as they allow very fast changes in the manner described.

Not sure how paywalled this is, but the Perspective in Science summarizes the research paper for a non-specialist audience and I think gives a better picture of what's new.
posted by mark k at 10:39 AM on October 24, 2022 [2 favorites]

Nice post and story, but I agree it's unfortunate the press release author used the phrase "junk DNA," as it's really not accurate. DNA broadly falls into two categories: that which codes for proteins, and that which doesn't. DNA that codes for proteins has come to be called "genes" (even though that's actually a much narrower and less useful definition that the original one, but that fight was lost before I was born), and DNA that doesn't is called "noncoding DNA."

Furthermore, noncoding DNA also falls into two (maybe three, maybe more depending on who you ask) broad categories: DNA which acts as regulatory sites for genes, and DNA with no known function (maybe telomeres and centrosomes could form a third category of "structural DNA," but a cell biologist would be better qualified to comment on that). I don't think anyone has ever considered noncoding DNA which acts as regulatory sites to be "junk DNA"; it is this final subcategory of DNA with no known function that gets that label.

Back in the '90s, and maybe into the '00s, there was a big debate over whether there was really any such thing as "junk" DNA, that is, whether the DNA without a known function actually had a function that we didn't know about. As time has passed, I think our (by which I mean cell biologists' and geneticists') understanding of regulatory DNA has improved, and it has become clearer that there is a fair amount of DNA that doesn't have a conventional role in regulating gene expression. Furthermore, studying the rates of evolution of these portions of the genome has found that selection basically doesn't act on this DNA, implying that mutations in these regions have no functional consequence to the organism. Biologists have also identified things like "jumping genes," which are almost like little bits of parasitic DNA that are able to replicate themselves within the genome while having no major functional effect on the organism, which suggests a mechanism for introducing and replicating "junk" DNA.

Anyway, I don't think any biologist today would consider noncoding, regulatory DNA to be "junk" DNA. Regulatory DNA has been at the center of research in genomics and cell biology for the last couple of decades or so. This paper is a really cool story, but it doesn't seem to be identifying a function for DNA that was previously thought to be functionless.
posted by biogeo at 6:36 PM on October 24, 2022 [3 favorites]