<p class="p1">How much of the human genome, our genetic blueprint, actually makes us who we are? New work by an evolutionary biologist at the University of Houston suggests that only<strong> up to 25%</strong> of the human genome is functional. The other 75% are so-called “junk DNA” - useless sequences that don’t play a role in the important chemical reactions inside us. This conclusion goes sharply against the estimate of <strong>80%</strong> functionality proposed by the <a href="https://www.encodeproject.org/" target="_blank">ENCODE project,</a> an international public research consortium that has led the way in human genome exploration.</p> <p class="p1"><a href="http://nsmn1.uh.edu/dgraur/" target="_blank">Dan Graur,</a> professor of biology and biochemistry, calculated that about <strong>10 to 15 percent</strong> of the genome is actually functional, with the upper limit of 25 percent.<span> </span></p> <p class="p1">His reasoning stems from looking at how mutations affect a population’s DNA. Graur’s mathematical model allowed him to calculate the <strong>“mutational load” </strong>- the total genetic load of a population that results from the accumulation of bad or <strong>deleterious</strong> mutations. At some point the load can become too much and the population would go extinct.<span> </span> </p> <p class="p1">Graur’s work related how reproductive success, the ability of a species to replenish itself, was decreased by the deleterious mutations. Over time, humans would have to reproduce at an impossible high rate to keep up with the mutations, Graur concluded.</p> <p class="p1">The professor explained why he finds the 80% functionality of the genome <a href="https://ghr.nlm.nih.gov/primer/genomicresearch/encode" target="_blank">proposed by the ENCODE scientists</a> as unrealistic:</p> <blockquote>
<p class="p3"><span class="s1">“For 80 percent of the human genome to be functional, each couple in the world would have to beget on average <strong>15 children</strong> and all but two would have to die or fail to reproduce,” <a href="http://www.uh.edu/news-events/stories/2017/JULY%2017/07142017Graur-functional-genome.php" target="_blank">writes Graur.</a> “If we use the upper bound for the deleterious mutation rate (2 × 10</span><span class="s2">−8</span><span class="s1"> mutations per nucleotide per generation), then … the number of children that each couple would have to have to maintain a constant population size would exceed the number of stars in the visible universe by ten orders of magnitude.”</span></p>
</blockquote> <p class="p5">This is not the first time Graur fought against the 80% claim. In a <a href="https://evolutionnews.org/2014/04/dan_graur_the_v/" target="_blank">2014 interview</a> with <em>Science</em> magazine, Graur even claimed its proponents are essentially pitching the idea of “intelligent design”. To Graur, asserting 80% usability implies that most of the genome exists to serve a purpose. Instead, he believes that “<span class="s3">everything is shaped by evolution,” a slow process that weeds out useless features through genetic mutations - the drivers of evolution. This process also accumulates a lot of junk in the human genome.</span></p> <p class="p5">Why is it important to know that only a quarter of the human genome may have functionality? Graur believes his work can shift the focus in the field of human genomics to what is useful from a medical standpoint: </p> <blockquote>
<p class="p3"><span class="s1">“We need to know the functional fraction of the human genome in order to focus biomedical research on the parts that can be used to prevent and cure disease,” <a href="http://www.uh.edu/news-events/stories/2017/JULY%2017/07142017Graur-functional-genome.php" target="_blank">said Graur</a>. “There is no need to sequence everything under the sun. We need only to sequence the sections we know are functional.”</span> </p>
</blockquote> <p class="p5">You can read the study <a href="https://academic.oup.com/gbe/article/3952726/An-upper-limit-on-the-functional-fraction-of-the?searchresult=1" target="_blank">here</a> in Genome Biology and Evolution.<span> </span></p>
Keep reading
Show less