Far fewer human genes exist than we once thought, scientists say

<body leftmargin="0" bgcolor="#000060" text="#FFFFFF" link="#FFFF00" vlink="#FF9900"> <b> <p class="MsoNormal"><font face="Arial" size="4">Far fewer human genes exist than we once thought, scientists say</font></p> </b> <p class="MsoNormal"><font face="Arial" size="1">Posted Oct. 25, 2004<br> Courtesy Nature<br> and World Science staff</font> </p> <b> <p class="MsoNormal"><font size="2" face="Arial">Ten years ago, scientists thought humans had about 100,000 genes. Today, they have trimmed that estimate by more than three quarters.</font></p> <p class="MsoNormal"><font size="2" face="Arial">The findings are part of a newly published analysis of the human genetic code. The authors of the analysis, an international group of researchers, say that in carrying out the project they have also begun to systematically pinpoint which genes set us apart from other animals. </font></p> <p class="MsoNormal"><font size="2" face="Arial">The findings are published in the Oct. 21 issue of the research journal <i>Nature</i>. In it, the researchers described the final product of the Human Genome Project, a 13-year effort to map out the genetic code that ended in 2003. </font></p> <p class="MsoNormal"><font size="2" face="Arial">In the <i>Nature</i> paper, the researchers reduced the estimated number of human genes to between 20,000 and 25,000.</font></p> <p class="MsoNormal"><font size="2" face="Arial">"Only a decade ago, most scientists thought humans had about 100,000 genes. When we analyzed the working draft of the human genome sequence three years ago, we estimated there were about 30,000 to 35,000 genes, which surprised many," said Francis S. Collins, director of the National Human Genome Research Institute in Bethesda, Md. "This new analysis reduces that number even further and provides us with the clearest picture yet of our genome." </font></p> <p class="MsoNormal"><font size="2" face="Arial">"The availability of the highly accurate human genome sequence in free public databases enables researchers around the world to conduct even more precise studies of our genetic instruction book and how it influences health and disease." <br> <br> One of the central goals of the effort to analyze the human genetic code is the identification of all genes. Genes are stretches of DNA containing code that allows the body to produce particular proteins, molecules that serve as the building blocks of the body. <br> <br> "The analysis found that some of the earlier gene models were erroneous due to defects in the unfinished, draft sequence of the human genome," said Jane Rogers, head of sequencing at the Wellcome Trust Sanger Institute in Hinxton, England.</font></p> <p class="MsoNormal"><font size="2" face="Arial">Although researchers are describing the new findings as the results of the "finished" project, it is not really quite finished. There still remain 341 gaps in scientists' description of the human genome sequence, although this is far fewer than the 150,000 gaps that there were four years ago. The technology now available cannot readily close the remaining gaps. This will require more research and new technologies, the researchers said. <br> <br> In addition to reducing the count of human genes, scientists reported that the improved quality of the finished human genome sequence, compared with earlier drafts, provides a much clearer picture of certain phenomena such as duplication of DNA segments and the "birth" and "death" of genes. <br> <br> Segmental duplications are large, almost identical copies of DNA present in at least two places in the human genome. In some cases these are duplicate copies of genes that, in other animals, exist in only one copy.  </font></p> <p class="MsoNormal"><font size="2" face="Arial">Researchers think that although these duplications may arise as evolutionary accidents, they can serve an important purpose because the organism uses them as a "laboratory" for creating genes with new functions. Once two identical genes appear where just one used to be, that frees one of them to mutate and take on new functions. </font></p> <p class="MsoNormal"><font size="2" face="Arial"> The high proportion of segmental duplication in the human genome shows our genetic material has undergone rapid innovation and change during the last 40 million years, presumably contributing to unique characteristics that separate us from our non-human primate ancestors. </font></p> <p class="MsoNormal"><font size="2" face="Arial">But some diseases are also associated with mutations in segmentally duplicated regions. </font></p> <p class="MsoNormal"><font size="2" face="Arial">"Now, through the unstinting efforts of groups around the world, this important and rapidly evolving part of our genome is open for scientific exploration," said Robert H. Waterston, chair of the Department of Genome Sciences at the University of Washington in Seattle. <br> <br> Segmental duplications cover 5.3 percent of the human genome, significantly more than in the rat genome, which has about 3 percent, or the mouse genome, which has between 1 and 2 percent. Segmental duplications provide a window into understanding how our genome evolved and is still changing. <br> <br> The accuracy of the finished human genome sequence produced by the Human Genome Project has also given scientists some initial insights into the "birth" and "death" of genes. </font></p> <p class="MsoNormal"><font size="2" face="Arial"> Scientists have identified more than 1,000 new genes that arose in the human genome after the lineage leading to humans separated from the one leading to rodents, some 75 million years ago. Most of these new genes arose through recent gene duplications and are involved with immune and reproductive functions. <br> <br> Researchers also used the finished human genome to identify 33 nearly intact genes that have recently acquired mutations, causing them to stop functioning, or "die." Scientists found that 10 of these appear to have coded for proteins involved in smell, which helps to explain why humans have a poorer sense of smell than rodents.<br> <br> The researchers also found that five of the genes that were inactive in humans were found to be still functional in chimpanzees. This could help researchers identify the key differences between humans and other primates, providing "fertile ground for future research projects," said Richard Gibbs, director of Baylor College of Medicine's Human Genome Sequencing Center in Houston. <br> <br> More than 2,800 researchers who took part in the International Human Genome Sequencing Consortium share authorship on the <i>Nature</i> paper, which expands upon the group's initial analysis published in Feb. 2001. </font></p> </b> <p class="MsoNormal"> <b> <font size="2" face="Arial"><a href="http://groups.yahoo.com/group/world-science">http://groups.yahoo.com/group/world-science</a></font> </b> </p> </body>