Junk DNA Might Play a Key Role in Evolutionary Dynamics

Scientists from Tel Aviv University have developed a new model that explains why junk DNA persists in living organisms and continues to exist alongside the original genome. The researchers call the phenomenon “border-induced selection,” which occurs when neutral sequences, such as junk DNA, reside near functional DNA.

Deletion events around the borders between junk and functional DNA are likely to damage functional regions. Their new model sheds light on the massive variety of genome sizes observed in nature and explains why neutral sequences are not eliminated from the genome of living creatures in nature, even millions of years later.

The researchers utilized dynamic simulations of insertions and deletions (indels) of short DNA segments and compared the resulting distributions of human intron lengths. The simulation results matched the distribution of lengths observed in nature. Additionally, they explained peculiar phenomena in the length distribution of introns, such as the significant variation in intron lengths and the distribution’s complex shape, which does not look like a standard bell curve.

The scientists explain that creatures’ genome size changes throughout evolution. For example, some salamander species have a genome ten times larger than the human genome. Previous studies showed that the rate of deletions is greater than the rate of additions in a variety of creatures, including bacteria, insects, and even mammals such as humans. The researchers aimed to determine how and why these genomes are not deleted, even when the probability of DNA deletion events is significantly greater than DNA addition events.

Gil Loewenthal, Ph.D. student and first author of the study, explains, “We have provided a different view to the dynamics of evolution at the DNA level.” While measuring the rate of indels in pseudogenes, which are relatively long sequences, more deletions occur, but they claim that in shorter neutral segments, deletions are likely to delete adjacent functional segments essential for functionality and are, therefore, rejected.

The new model’s significance lies in the understanding of the various sizes of DNA and why junk DNA exists alongside functional DNA. With a better understanding of evolution at the DNA level, the researchers hope to uncover more about the development of living organisms in nature. The study was published in the journal Open Biology.