The mutation responsible for the change was not in protein-coding genes, which comprise a relatively tiny fraction of the genome, but in a section of the vast (and until recently, thought to be “junk”) non-coding portion of the genome, which plays a key role in gene expression.

“This is a remarkable finding because such a tiny change – just one DNA letter out of ~2.8 billion – was enough to produce a dramatic developmental outcome,” Nitzan Gonen from the Goodman Faculty of Life Sciences and Institute of Nanotechnology and Advanced Materials at Bar-Ilan University said in a press release. “It shows that non-coding DNA can have a profound effect on development and disease.”