Researchers discover European genetic twist By Nicholas Wade The New York Times Monday, January 17, 2005
Researchers in Iceland have discovered a region in the human genome that, among Europeans, appears to promote fertility, and maybe longevity as well. . Although the region, a stretch of DNA on the 17th chromosome, occurs in people of all countries, it is much more common in Europeans, as if its effect is set off by something in the European environment. A further unusual property is that the DNA region has a much more ancient lineage than most human genes; the researchers suggest, as one possible explanation, that it could have been inserted into the human genome through interbreeding with one of the archaic human lineages that developed in parallel with that of modern humans. . The genetic region was discovered by scientists at DeCode Genetics of Reykjavik, who have made the Icelandic population, with its comprehensive genealogy and medical records, a prime hunting ground for the genetic roots of common diseases. Their finding is published in the Monday issue of Nature Genetics in a report by Kari Stefansson, Augustine Kong, Hrein Stefansson and other DeCode scientists. . The report seems likely to receive considerable attention, even though it raises as many questions as it answers. "I thought it was one of the most interesting papers in population genetics I have ever read," said Nick Patterson, a mathematician at the Broad Institute in Cambridge, Massachusetts, who advised DeCode on the article but has no other connection with the company. . The region came to light in the search for a schizophrenia-causing gene, which turned out not to be there. But the DeCode researchers noticed that the DNA sequences they had examined did not seem to agree with those in the standard human genome sequence, said Kari Stefansson, DeCode's chief executive. . The lack of agreement turned out to be caused by the fact that the region exists in two forms in the Icelandic population. The region is not a single gene but a vast section of DNA, some 900,000 units in length, situated in the 17th of the 23 pairs of human chromosomes. In some Icelanders, the DeCode team found, the section runs in the standard direction, but in others it is flipped. Looking for any physical consequence, the DeCode researchers found that women carrying the flipped or inverted section tend to have slightly more children. . The section carries several known genes, none of which have any obvious connection with fertility. It is not clear why inverting the section should have any effect on the number of children, Stefansson said. But the inversion does increase the rate of recombination, the shuffling of genes between generations that is a major source of genetic novelty. That could account for some of the increase in fertility. . The DeCode scientists found that the chromosome 17 inversion is rare in Africans, almost absent in Asians, but is possessed by 20 percent of Europeans, the same frequency as in Iceland. The inversion seems to have been favored by natural selection among Europeans in fairly recent times, perhaps the past 10,000 years. . "Maybe something switched it on in the European environment, such as an interaction with diet," said David Reich, a population geneticist at the Broad Institute. . Stefansson said that another property of the inversion, though one not described in the new Nature Genetics article, is that it is associated with longevity. DeCode scientists have located two sites on Icelanders' genomes where there is some genetic variant that promotes longer life span. The chromosome 17 inversion, it turns out, lies at one of these sites. It occurs at much higher frequency in women over 95 and in men over 90 than in the normal population. "It seems to confer on people the ability to live to extreme old age," Stefansson said. . It is particularly surprising that the same genetic element should promote fertility and longevity since most organisms are obliged to follow a strategy either of breeding fast during short lives or of living longer and having fewer children. "Usually people think of there being a trade-off between fertility and longevity," said Alan Rogers, a population geneticist at the University of Utah. . "So we are getting a free lunch here." . Fertility is doubtless affected by different genes in different populations and DeCode has found one special to Europeans because that is where it was looking. The increased frequency of the inversion in Europeans is one of a growing number of examples of recent human evolution. . The inversion itself, however, is surprisingly ancient. Its age is revealed by its counterpart, the standard or noninverted section of chromosome 17. . The standard and inverted regions cannot exchange genetic elements during recombination because their DNA sequences do not match. Hence, unlike most of the rest of the genome, which gets shuffled in each generation, the two forms have enjoyed a separate existence since their creation. This event presumably happened when the region came adrift from its parent chromosome and got knitted back in the wrong way round. . When all the known versions of a human gene are compared, in most cases they turn out to have had a single common ancestor about a million years ago. But the standard and flipped version of the chromosome 17 region last shared a common ancestor three million years ago. [Non-text portions of this message have been removed] ------------------------ Yahoo! Groups Sponsor --------------------~--> Give underprivileged students the materials they need to learn. Bring education to life by funding a specific classroom project. http://us.click.yahoo.com/4F6XtA/_WnJAA/E2hLAA/BRUplB/TM --------------------------------------------------------------------~-> *************************************************************************** Berdikusi dg Santun & Elegan, dg Semangat Persahabatan. Menuju Indonesia yg Lebih Baik, in Commonality & Shared Destiny. www.ppi-india.uni.cc *************************************************************************** __________________________________________________________________________ Mohon Perhatian: 1. Harap tdk. memposting/reply yg menyinggung SARA (kecuali sbg otokritik) 2. Pesan yg akan direply harap dihapus, kecuali yg akan dikomentari. 3. Lihat arsip sebelumnya, www.ppi-india.da.ru; 4. Satu email perhari: [EMAIL PROTECTED] 5. No-email/web only: [EMAIL PROTECTED] 6. kembali menerima email: [EMAIL PROTECTED] Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/ppiindia/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
