Tel Aviv University researchers say they have developed a new model that offers a possible solution to the scientific question of why neutral sequences, sometimes referred to as “junk DNA”, are not eliminated from the genome of living creatures in nature and continue to exist within it even millions of years later. This has to do with the huge variety of sizes of DNA in nature. According to the researchers, “junk DNA” hides in functional areas, thus deletions are likely to damage the functional DNA and therefore are rejected by evolution.
Junk DNA is often located in the vicinity of functional DNA. Deletion events around the borders between junk and functional DNA are likely to damage the functional regions and so evolution rejects them. The model contributes to the understanding of the huge variety of genome sizes observed in nature.
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The phenomenon that the new model describes is called by the team of researchers “border induced selection”. It was developed under the leadership of the PhD student Gil Loewenthal in the laboratory of Prof. Tal Pupko from the Shmunis School of Biomedicine and Cancer Research, Faculty of Life Sciences and in collaboration with Prof. Itay Mayrose (Faculty of Life Sciences, Tel Aviv University). The study was published in the journal “Open Biology”.
The researchers explain that throughout evolution, the size of the genome in living creatures in nature changes. For example, some salamander species have a genome ten times larger than the human genome.
Prof. Pupko explains: “The rate of deletions and short insertions, which are termed in short as ‘indels’, is usually measured by examining pseudogenes. Pseudogenes are genes that have lost their function, and in which there are frequent mutations, including deletions and insertions of DNA segments. In previous studies that characterized the indels, it was found 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 question we tried to answer is how the genomes are not deleted when the probability of DNA deletion events is significantly greater than DNA addition events.”