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  3. Researchers have reconstructed an ancient human genome (基因组) for the first time, thanks to the discovery of a 4000-year-old stra

Researchers have reconstructed an ancient human genome (基因组) for the first time, thanks to the discovery of a 4000-year-old stra

admin2017-06-29  50
问题     Researchers have reconstructed an ancient human genome (基因组) for the first time, thanks to the discovery of a 4000-year-old strand of hair in Greenland permafrost (永冻土). Experts say that similar techniques could be employed in many other ways, such as analyzing the DNA of South American mummies or crime victims.
    The sample was taken from one of four strands of hair collected in Greenland by Danish archaeologists in the 1980s. The hairs are the only known human remains from the earliest people to settle in Greenland. A chance conversation alerted University of Copenhagen researcher Eske Willerslev, who was just back from two unsuccessful months in Greenland searching for human remains to test for DNA, to the sample, which had been stored at the National Museum of Denmark for more than 20 years.
    Once they had the hairs in their possession, Willerslev and colleagues set about sequencing the sample. The team used dozens of sequencing machines to identify and map DNA fragments in the hair shafts, a process that took nearly 2 months. The data revealed more than 80% of the genome, coverage comparable to what can be done with a modern human genome.
    "From the DNA, we can tell a lot about the individual," says Willerslev. "He had brown eyes, brown skin, a tendency to baldness, and dry earwax." The researchers have named him "Inuk," which means "man" or "human" in Greenlandic.
    The genome also sheds light on where the man’s relatives came from. When the researchers compared his DNA with that collected from more than 40 Arctic and native North American populations, they concluded that the first people to settle in Greenland were related to groups now living in northeastern Siberia. The analysis also revealed that these first colonists were not the ancestors of the Inuit who live on the island now.
    The researchers say that when it comes to ancient DNA, the Greenland sample may amount to low-hanging fruit. The hair had been preserved by cold for thousands of years, ideal conditions for recovering DNA. "Working with these young permafrost samples is worlds apart from working with older, non-permafrost samples," says Adrian Briggs, a researcher at the Max Planck Institute. He notes that the Greenland sample contains tens of thousands of times more DNA than typically found in Neandertal and early modern human samples from warmer environments.
    Yet the discovery shows that with ever-cheaper genetic sequencing and faster computers, it is possible to recover a full nuclear DNA sequence from an ancient human, even when the genome is broken into tiny fragments. The nicest thing this paper shows is that the application of next-generation sequencing techniques is really going to expand what we can do with ancient DNA.
By saying that the Greenland sample may be "low-hanging fruit" (Line 1-2, Para. 6), the researchers meant that _____.
选项 A、the sample was favorable for their test
B、the sample made the test more difficult
C、the sample brought about little benefits
D、the sample produced unexpected results
答案A
解析 从第6段第2句中的ideal和最后一句中的tens of thousands of times more DNA等可知研究人员认为格陵兰岛的样本对他们的研究带来非常积极的帮助，因此，本题应选A。
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