一國際研究小組最近宣稱,，他們最新完成了迄今為止年代最為久遠的史前生物的基因測序工作,，成功獲得距今70萬年的古代野馬的基因組序列。這是科學家首次完成對中更新世時期物種的基因測序工作,。
更新世,，又稱洪積世，是地質時代第四紀的早期,，距今180萬年到11000年左右,，其顯著特征是氣候變冷，有冰期與間冰期的明顯交替,，而這一時期的大多數(shù)動植物屬種則與現(xiàn)代相似,。在該項研究中,，科學家所研究的對象即是來自加拿大西北部育空地區(qū)永久凍土中發(fā)現(xiàn)的70萬年前的野馬骨骼殘骸,。
在有機體死亡之后，其化石中會殘留該物種的DNA分子,，雖然不可能是整個的基因組,，但殘留的DNA片段仍有機會被重新組合起來。如果有足夠的DNA片段殘留下來,，科學家就可以重建消失物種的完整基因組序列,。在過去幾年間，科學家已經(jīng)獲得了一些古人類的完整基因組序列,，但從時間上看,，則遠遠沒有70萬年這樣久遠。70萬年這一時間比之前DNA測序物種最早年份記錄提高了大約10倍,。
利用基因測序,，科學家能夠進一步了解過去70萬年馬血統(tǒng)進化過程中的主要基因變化情況。他們可以追蹤史前野馬向近代馬種轉變過程中基因的變化,，以獲得現(xiàn)代馬匹基因構成的詳細信息,。通過對70萬年前的史前野馬、43000年前的古代馬,、六個現(xiàn)代馬種以及驢的基因組進行對比研究,，科學家發(fā)現(xiàn)，所有現(xiàn)代馬科動物都有一個共同的祖先,，生活在400萬至450萬年前,。這一發(fā)現(xiàn)表明，馬,、驢以及斑馬的最初進化起源時間,或者說地球上第一匹野馬的出現(xiàn)時間,，遠比之前科學家所認知的要早。
該項研究由丹麥自然歷史博物館科學家領導完成,，研究小組成員則包括來自丹麥,、中國,、加拿大、美國,、瑞士,、英國、挪威,、法國,、瑞典和沙特阿拉伯十個國家的科學家，其成果刊發(fā)在最新出版的《自然》雜志上,。（生物谷 Bioon.com）
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生物谷推薦的英文摘要
Nature doi:10.1038/nature12323
Recalibrating Equus evolution using the genome sequence of an early Middle Pleistocene horse
Ludovic Orlando, Aurélien Ginolhac, Guojie Zhang, Duane Froese, Anders Albrechtsen, Mathias Stiller, Mikkel Schubert, Enrico Cappellini, Bent Petersen, Ida Moltke, Philip L. F. Johnson, Matteo Fumagalli, Julia T. Vilstrup, Maanasa Raghavan, Thorfinn Korneliussen, Anna-Sapfo Malaspinas, Josef Vogt, Damian Szklarczyk, Christian D. Kelstrup, Jakob Vinther, Andrei Dolocan, Jesper Stenderup, Amhed M. V. Velazquez, James Cahill, Morten Rasmussen, Xiaoli Wang, Jiumeng Min, Grant D. Zazula, Andaine Seguin-Orlando, Cecilie Mortensen, Kim Magnussen, John F. Thompson, Jacobo Weinstock, Kristian Gregersen, Knut H. Røed, Véra Eisenmann, Carl J. Rubin, Donald C. Miller, Douglas F. Antczak, Mads F. Bertelsen, Søren Brunak, Khaled A. S. Al-Rasheid, Oliver Ryder, Leif Andersson, John Mundy, Anders Krogh, M. Thomas P. Gilbert, Kurt Kjær, Thomas Sicheritz-Ponten, Lars Juhl Jensen, Jesper V. Olsen, Michael Hofreiter, Rasmus Nielsen, Beth Shapiro, Jun Wang & Eske Willerslev
The rich fossil record of equids has made them a model for evolutionary processes1. Here we present a 1.12-times coverage draft genome from a horse bone recovered from permafrost dated to approximately 560–780 thousand years before present (kyr BP)2, 3. Our data represent the oldest full genome sequence determined so far by almost an order of magnitude. For comparison, we sequenced the genome of a Late Pleistocene horse (43 kyr BP), and modern genomes of five domestic horse breeds (Equus ferus caballus), a Przewalski’s horse (E. f. przewalskii) and a donkey (E. asinus). Our analyses suggest that the Equus lineage giving rise to all contemporary horses, zebras and donkeys originated 4.0–4.5 million years before present (Myr BP), twice the conventionally accepted time to the most recent common ancestor of the genus Equus4, 5. We also find that horse population size fluctuated multiple times over the past 2 Myr, particularly during periods of severe climatic changes. We estimate that the Przewalski’s and domestic horse populations diverged 38–72 kyr BP, and find no evidence of recent admixture between the domestic horse breeds and the Przewalski’s horse investigated. This supports the contention that Przewalski’s horses represent the last surviving wild horse population6. We find similar levels of genetic variation among Przewalski’s and domestic populations, indicating that the former are genetically viable and worthy of conservation efforts. We also find evidence for continuous selection on the immune system and olfaction throughout horse evolution. Finally, we identify 29 genomic regions among horse breeds that deviate from neutrality and show low levels of genetic variation compared to the Przewalski’s horse. Such regions could correspond to loci selected early during domestication.
