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Monday, November 20, 2023

Two Heidelberg graduate students reject junk DNA

Science in School is a magazine for European science teachers. Two graduate students1 have just published an article in the November issue: Not junk after all: the importance of non-coding RNAs.

Note: The article has been edited to remove some of the references to junk DNA and the editor has added the following disclaimer to the end of the article: Editor’s note: Some parts of the introduction and conclusion were rephrased to avoid any misunderstanding concerning the nature of ‘junk DNA’, which is not the focus of this article. Here's a link to the revised article: Not junk after all: the importance of non-coding RNAs. More changes are expected.

Not junk after all: the importance of non-coding RNAs

Originally assumed to be useless ‘junk DNA’, sections of the genome that don’t encode proteins have been revealed as a source of many important non-coding RNA structures.

The central dogma of molecular biology is that DNA is used as a template to create messenger RNA (mRNA), which in turn is translated into proteins that build the tissues in our bodies and carry out the main functions of our cells and organs. In other words, DNA → mRNA → proteins. Interestingly, though, only 2% of the DNA in our whole genome codes for proteins! So, what does the other 98% of the human genome do? In the mid-1900s, it was widely believed that a great part of our genome was useless, repetitive ‘junk DNA’. However, this belief goes against the evolution theory, which suggests that useless sequences would be eliminated from the genome since their maintenance requires energy. In the late 20th century and the early 21st century, this junk DNA has been shown to not only contain important regulatory elements for transcription, but also sequences that encode various non-coding RNAs that have functions in many cellular mechanisms.

I just finshed a podcast interview with Kat Arney and one of the questions she asked was what is the most important thing I'd like scientists to know about this topic. I picked evolution—I'd like modern researchers to understand that there's more to evolution than natural selection. You can see the problem in this example where two students who are working toward a Ph.D. at a top lab in Europe think that junk DNA "goes against the evolution theory."

That's sad. It's also sad that these two students think that 98% of our genome might be devoted to regulation and non-coding genes.

We need to focus on educating the next generation of scientists and that starts with educating science teachers. This is not the way to do it.

Here's the contact information for Science in School. I've written the editor at Please send a message if you are as concerned about the spread of scientific misinformation as I am.

Zuzana Koskova at the European Molecular Biology Laboratory in Heidelberg (Germany) and Miguel Hernandez at the University Hospital, Heidelberg. I tried sending an email message to Zuzana Koskova but got no reply. I was unable to find contact information for Miguel Hernandez.


Anonymous said...

I have a question

I've recently fond your blog, and i'm somehow new with the junk-dna debate, if in uderstan correctly you suggest that the only part of our genome that is relevant is the coding one. But reding from Sean B Carroll and other evo-devo litterature i understand that Cis-regulatory elements that are parts of the non-coding dna do play vers important works in developpement and evolution don' that clash with tour views?

Larry Moran said...


The concept of junk DNA has been around for more than 50 years. The original proponents of junk DNA knew about regulatory sequences and so did I. They also knew about other functional non-coding DNA. At no time in the past 50 years did I, or any knowledgeable scientist, ever say that all non-coding DNA was junk. From the very beginning, the view was that about 1% of the human genome is coding and another 9% is functional non-coding DNA. The rest (90%) is junk.

Anonymous said...

So you're basiccaly accepting pretty much most of those regulatory networks described by the evo-devo folks? I say this because i've seen that Jerry coyne was skeptical of any major role of cis elements

Graham Jones said...

Planaria are famous for their regeneration abilities. I only learned recently that they also have super-sloppy genomes. From Levin's paper (

"... not only are some planarian species mixoploid (not every cell has the same chromosome number) [46], but they also accumulate immense amount of change: up to 74% in protein-coding genes [47]. Indeed, large numbers of mutations have been found both outside and within gene-coding regions, including many amino acid substitutions and non-synonymous SNPs. Furthermore, a recent analysis of the genome of the planaria Schmidtea mediterranea revealed that many essential genes appear to be missing from the genome, including components of many core pathways ranging from cell division, to DNA repair and metabolism [48]. And yet, these animals regenerate under control conditions with 100% anatomical fidelity, making perfect planaria each time despite their messy genomes."

Perhaps biology courses should have a bit less about C. elegans genomes and a bit more about planarian genomes.

Anonymous said...

Under what criteria is it considered "messy".

Anonymous said...

"but they also accumulate immense amount of change: up to 74% in protein-coding genes" seems to be a grammatical error. If you follow through to the cited work, it turns out that 74% OF protein-coding genes contain point mutations (they write SNPs, but I think that the polymorphism is at the level of the population rather than the individual), many of which I presume to be silent. Writing IN suggests mutation of a gene to beyond the point of recognition.

Anonymous said...

I’ve been reading the blog for a while and long been convinced about junk DNA. But I don’t remember seeing the ratios. I was under the mistaken impression that there was less functional non coding DNA than coding DNA. Nine times more is huge. Is this similar across species? Perhaps highlighting this number would help reduce the number of people misunderstanding the issue

Larry Moran said...

@anonymous: Here's a summary of what we know about functional DNA in the human genome.

What's in Your Genome: Chapter 5 - The Big Picture