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An international team has discovered that each species of primates, including humans, has an enormous amount of unique fragments in its genome. The study, involving two researchers at the Institute of Evolutionary Biology (joint center of the University Pompeu Fabra and the Consejo Superior de Investigaciones Científicas), helps to understand the mechanisms of human evolution and the basis of various diseases are unique in its kind. The research is published in
Nature, a special edition dedicated to the celebration of the bicentenary of the birth of the English naturalist Charles Darwin.

During the last decade, the scientific community has accepted the hypothesis that humans and their closest living relatives, chimpanzees, differed at only 1.24% of their DNA sequences. However, the findings of this study show that this estimate is incorrect and that in fact the number of differences can be up to 10 times higher.

Tomàs Marques-Bonet, Institute of Evolutionary Biology (Joint Research Center of the University Pompeu Fabra and CSIC), has coordinated the international team, led by Evan E. Eichler, University of Washington (Seattle, USA), in close collaboration with Arcadi Navarro (ICREA Barcelona-IBE).

According to the authors, the key to this discovery has resided in the study of segmental duplications, large fragments of DNA repeated many times throughout the genome. So far, this part of the genome was ignored because it was very complicated individually from the rest of the DNA. However, long suspected that his presence was an important feature.

The international team has systematically studied the segmental duplications of the entire genome of four species of primates: macaques, orangutans, chimpanzees and humans. This will not only could produce the first comprehensive catalog of species-specific regions of the genome, but also far better quantify the differences between species and to understand at what stage of evolution appeared.

Research reveals qualitatively different evolutionary novelty. As the researchers, the differences had been worked with so far were changes (mutations) in the sequences of the genome shared by all primates. The authors explain this with a simile: changes would be equivalent to having different editions of a book.

However, several studies by researchers at the Institute of Evolutionary Biology differences are unique to each species. Following the same analogy, it would be radical differences in the library of every kind are collections of books and some other agencies have not.

Segmental duplications are fragments of the genome, thousands of millions of nucleotides long, which have doubled due to very complex molecular mechanisms. That is, at certain times of evolution, made multiple copies were inserted in various parts of the genome. As the duplications can be quite large, often containing complete genes. Copies of these genes, which are identical in principle, can be specialized based on acquiring small mutations, to completely differentiated from each other.

Thus, generating the majority of genes unique to a particular species: by duplication and subsequent specialization. All these new genes may perform new functions that are unique to the species that have them. As explained Arcadi Navarro and Tomàs Marqués, duplications predispose the genome to reorganize itself, to have major structural changes, such as who makes the same building with different rooms. This phenomenon can lead to diseases such as autism, schizophrenia or mental retardation. But scientists point out that duplication of genes is not synonymous with failure, but to change and novelty. News that may be favored by natural selection or may be pathological, depending on how they develop.

In addition to identifying these differences, the study has also succeeded in dating the time that there was more overlap. They fall in the interval between 8 and 12 million years ago, just before the separation of the lineages of humans and chimpanzees, which occurred some six million years ago. This fact implies that all the genes studied, which has just appeared, have acquired new features along the six million years of leading men and chimps separated evolutionarily.

For Marques and Navarro, probably because of this separation is that humans managed to adapt to current environment. The researchers acknowledge that, perhaps, is in this vast ocean of difference where to find the so-called human genes or genes that lead to certain diseases of the human species. For now, researchers know whether this research will reveal these points.