下载亿题库APP
联系电话:400-660-1360
请谨慎保管和记忆你的密码,以免泄露和丢失
请谨慎保管和记忆你的密码,以免泄露和丢失
1. Washing, brushing and varnishing fossils — all standard conservation treatments used by many fossil hunters and museum curators alike — vastly reduces the chances of recovering ancient DNA.
2. Instead, excavators should be handling at least some of their bounty with gloves, and freezing samples as they are found, dirt and all, concludes a paper in the Proceedings of the National Academy of Sciences today.
3. Although many palaeontologists know anecdotally that this is the best way to up the odds of extracting good DNA, Eva-Maria Geigl of the Jacques Monod Institute in Paris, France, and her colleagues have now shown just how important conservation practices can be. This information, they say, needs to be hammered home among the people who are actually out in the field digging up bones.
4. Geigl and her colleagues looked at 3,200-year-old fossil bones belonging to a single individual of an extinct cattle species, called an aurochs. The fossils were dug up at a site in France at two different times — either in 1947, and stored in a museum collection, or in 2004, and conserved in sterile conditions at -20 oC.
5. The team's attempts to extract DNA from the 1947 bones all failed. The newly excavated fossils, however, all yielded DNA.
6. Because the bones had been buried for the same amount of time, and in the same conditions, the conservation method had to be to blame says Geigl. "As much DNA was degraded in these 57 years as in the 3,200 years before," she says.Wash in, wash out
7. Because many palaeontologists base their work on the shape of fossils alone, their methods of conservation are not designed to preserve DNA, Geigl explains.
8. The biggest problem is how they are cleaned. Fossils are often washed together on-site in a large bath, which can allow water — and contaminants in the form of contemporary DNA — to permeate into the porous bones. "Not only is the authentic DNA getting washed out, but contamination is getting washed in," says Geigl.
9. Most ancient DNA specialists know this already, says Hendrik Poinar, an evolutionary geneticist at McMaster University in Ontario, Canada. But that doesn't mean that best practice has become widespread among those who actually find the fossils.
10. Getting hold of fossils that have been preserved with their DNA in mind relies on close relationships between lab-based geneticists and the excavators, says palaeogeneticist Svante P??bo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. And that only occurs in exceptional cases, he says.
11. P??bo's team, which has been sequencing Neanderthal DNA, continually faces these problems. "When you want to study ancient human and Neanderthal remains, there's a big issue of contamination with contemporary human DNA," he says.
12. This doesn't mean that all museum specimens are fatally flawed, notes P??bo. The Neanderthal fossils that were recently sequenced in his own lab, for example, had been part of a museum collection treated in the traditional way. But P??bo is keen to see samples of fossils from every major find preserved in line with Geigl's recommendations — just in case. Warm and wet
14. Much human cultural development took place in temperate regions. DNA does not survive well in warm environments in the first place, and can vanish when fossils are washed and treated. For this reason, Geigl says, most ancient DNA studies have been done on permafrost samples, such as the woolly mammoth, or on remains sheltered from the elements in cold caves — including cave bear and Neanderthal fossils.
15. Better conservation methods, and a focus on fresh fossils, could boost DNA extraction from more delicate specimens, says Geigl. And that could shed more light on the story of human evolution.(640 words nature )
Glossary Palaeontologists 古生物学家Aurochs 欧洲野牛Neanderthal (人类学)尼安德特人,旧石器时代的古人类。
雅思考试总分是多少?:雅思考试总分是多少?雅思满分是9分,最低分是0分。其实各个国家和各个学校对雅思的要求都是不同的,像去读澳大利亚,就必须要考雅思,最少要考到5.5分,这是留学这个国家的规定。好的学校要求的雅思分数要高一点,不好的要求要低一点,像大家都熟悉的牛津大学和剑桥大学对雅思的要求最低都要7.5分。
雅思考试有几种类型?:雅思考试有几种类型?雅思考试分学术类和培训类两种,分别针对申请留学的学生和计划在英语语言国家参加工作或移民的人士。考试分听、说、读、写四个部分,总分9分。
雅思考试内容有哪些?:雅思考试内容有哪些?雅思考试分为听力、阅读、口语、写作四个部分,一般需要两天时间。第一天的上午,全体考生都要参加相继进行的听力、阅读、写作三项考试;第一天的下午和第二天上午陆续举行口语考试。
2020-06-01
2020-06-01
2020-06-01
2020-06-01
微信扫码关注公众号
获取更多考试热门资料