healthHealth and Medicine

Some Of Our "Junk DNA" Is Actually Very Important For Our Genitals


Tom Hale


Tom Hale

Senior Journalist

Tom is a writer in London with a Master's degree in Journalism whose editorial work covers anything from health and the environment to technology and archaeology.

Senior Journalist

This discovery was first hinted at thanks to a mouse called Randy. u3d/Shutterstock

A massive chunk our DNA doesn’t actually appear to contain genes that code for proteins, leading to the nickname “junk DNA”. However, that doesn't mean it should be chucked into the trash.

Scientists in the UK have now discovered that a small snippet of this so-called junk DNA actually does something extremely important: It changes the genitals you’re born with. Not only does this shed some light on our much-misunderstood junk DNA, but it may even explain sex development in humans.


This discovery was first hinted at thanks to a mouse called Randy. In 1991, a chromosomally female mouse (with two X chromosomes) developed male testes when a team of scientists introduced a certain gene, called Sry, into the developing embryo.

They discovered this change was due to a protein called SOX9, which determines whether a mammal will develop ovaries or testes. At a key stage in development, low amounts of SOX9 lead to ovaries, higher amounts lead to testes.

The amount of SOX9 produced is initially controlled by the Sry gene. Only males, who have an X and a Y chromosome, will develop testes since this Sry gene is located on the Y chromosome. On the other hand, females have two X chromosomes, so they don’t make enough SOX9 to spark the change.

As reported in the journal Science, this new study dives deeper into this evidence by introducing a small piece of DNA called enhancer 13 (Enh13), which was discovered over half a million bases away from the Sry gene. Much like the rest of the genome's “junk DNA”, Enh13 does not carry any genes that are used to make proteins.


When Enh13 was removed from male mice embryos, they developed ovaries and female genitalia. As an enhancer, Enh13 works by boosting the expression of the Sry gene by increasing the likelihood of its transcription. Usually, it takes a few different changes to have a large effect, so it’s pretty surprising to see that Enh13 alone can have a profound effect on an embryo's sex.

Enh13 is located in the part of the mouse genome that maps directly onto a region of the human genome, so the scientists expect a similar effect in humans too.

“Our study also highlights the important role of what some still refer to as 'junk' DNA, which makes up 98 percent of our genome. If a single enhancer can have this impact on sex determination, other non-coding regions might have similarly drastic effects,” first author Dr Nitzan Gonen, a postdoctoral researcher at the Francis Crick Institute, said in a statement

“For decades, researchers have looked for genes that cause disorders of sex development but we haven't been able to find the genetic cause for over half of them. Our latest study suggests that many answers could lie in the non-coding regions, which we will now investigate further."


healthHealth and Medicine
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  • DNA,

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  • sex determination,

  • junk DNA,

  • ovaries