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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

admin2023-02-20  12
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.
When Eske Willerslev decided to test the strands of hair for DNA, ________.
选项 A、he discovered the hair by chance
B、the hair was found by him in Greenland permafrost
C、he failed in all the previous tests
D、the hair was kept in National Museum of Denmark
答案D
解析 原文该句提到的sample指的就是“头发”的样本，末尾的定语从句表明该头发样本当时收藏在丹麦国家博物馆中，因此，本题应选D。A中的by chance与第2段最后一句的chance同为“偶然”的意思，但原文提到的是一坎“偶然的”谈话，与头发的发现是否偶然无关，而且第2段第1句表明这些头发样本是由丹麦考古学家采集的，并非Eske Willerslev发现的。因此A和C均不正确；第2段最后一句中的unsuccessful months只表明Eske Willerslev没能成功地在格陵兰岛寻找到古人的遗骸用于DNA测试，来提及他之前与DNA有关的测试，B与文意不符。
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