據(jù)physorg網(wǎng)站2007年10月10日?qǐng)?bào)道,，美國(guó)威斯康辛大學(xué)麥迪遜分校研究人員發(fā)現(xiàn)了分子所具有的一項(xiàng)絕技,，他們?cè)诨驅(qū)用嫔显敿?xì)闡述了自然選擇的過(guò)程,。
霍華德.休醫(yī)學(xué)研究所研究員肖恩.B.卡羅爾和前美國(guó)威斯康辛大學(xué)麥迪遜分校研究生克里斯.托德.黑亭基爾在《自然》雜志上撰寫(xiě)了一篇論文，詳細(xì)闡述了單個(gè)酵母基因是如果在許多代時(shí)間內(nèi)分裂成兩個(gè),，以便更加有效地適應(yīng)環(huán)境,。他們的研究顯示，基因分裂是推動(dòng)進(jìn)化的最基本動(dòng)力,?？_爾是全球著名的進(jìn)化生物學(xué)家，他說(shuō),，“這是新能力出現(xiàn),，新功能進(jìn)化發(fā)展的原因。蝴蝶,、大象和人類(lèi)身上正在發(fā)生這種變化,。進(jìn)化一直在進(jìn)行之中。”
此項(xiàng)研究意義重大,，是因?yàn)樗屛覀儚淖罨鶎用媪私饬松矬w變得更加適應(yīng)他們所處環(huán)境的方式,。研究為我們揭示了自然選擇的工作方式。自然選擇這一重要的理論最先由查爾斯.達(dá)爾文提出,，達(dá)爾文認(rèn)為積聚無(wú)規(guī)則變化,，然后量變引發(fā)質(zhì)變,，從而提升生物體的生存能力，被自然“選擇”遺傳給未來(lái)后代,。
此項(xiàng)新研究重新演示了1億年前或幾年前酵母系列基因的改變,，當(dāng)一個(gè)關(guān)鍵基因被復(fù)制時(shí)，它會(huì)將它的營(yíng)養(yǎng)處理反應(yīng)分開(kāi)來(lái),，以便更好地利用酵母所依賴(lài)的食物,，即糖。
卡羅爾說(shuō),，“我們發(fā)現(xiàn)的一個(gè)嶄新東西就是基因復(fù)制,。當(dāng)你有一個(gè)基因的兩個(gè)復(fù)制品時(shí)，有利改變可能就會(huì)出現(xiàn),，使一個(gè)或兩個(gè)復(fù)制基因能夠出現(xiàn)新的功能,，并保留老的功能。這一現(xiàn)象將每時(shí)每刻在每一個(gè)活的生物體中發(fā)生,。我們當(dāng)中的許多人正攜帶有復(fù)制基因,，只是我們并沒(méi)有意識(shí)到這些基因復(fù)制的開(kāi)始和結(jié)束。”
卡羅爾稱(chēng),，簡(jiǎn)爾言之,，兩個(gè)基因可能比一個(gè)更好，這正如多余勞動(dòng)力會(huì)促使勞動(dòng)力分工一樣,?；蚰軌蜃龊芏嗍虑椋瑥?fù)制添加一個(gè)新的遺傳源,，這一新遺傳源可以分擔(dān)工作量或新添功能,。比如，就人而言,，我們能夠看到顏色,，需要我們具有不同的分子接受器，以辨別紅色和綠色的差別,，但是這兩種分子接受器可能都來(lái)源于相同的視覺(jué)基因,。卡羅爾稱(chēng)觀(guān)測(cè)進(jìn)化進(jìn)程的難點(diǎn)在于自然遺傳改變經(jīng)常是非常緩慢的,，化學(xué)堿基對(duì)的微小改變就需要基因數(shù)千至數(shù)百萬(wàn)年的日積月累,。
測(cè)量此類(lèi)微小改變需要一種像簡(jiǎn)單的啤酒酵母一樣的生物體模型，在相當(dāng)短的一段時(shí)間內(nèi)就可以產(chǎn)出大量后代,?？_爾稱(chēng)，酵母是非常完美的,，因?yàn)樗麄兊纳衬芰κ惯z傳改變研究能夠更加深入,，獲得更加精確的研究成果,，研究人員可能生產(chǎn)和快速計(jì)算大量生物體的基因改變情況。如果對(duì)果蠅這種生物學(xué)最佳模型進(jìn)行相同研究,，則需要能夠裝滿(mǎn)一個(gè)足球場(chǎng)的果蠅,，且工作量也要多年時(shí)間。
卡羅爾稱(chēng),，“在非常微小的進(jìn)化中,，基因分裂過(guò)程往往會(huì)變得更好。當(dāng)經(jīng)過(guò)一段時(shí)間后,，這些非常微小的變化將使一群生物體獲得成功,，他們將把其它生物體淘汰出局。”
新研究從不同地區(qū)的酵母中提取出基因組,，以評(píng)估他們對(duì)孿生基因表現(xiàn)的影響力,，同時(shí)對(duì)另外一個(gè)僅保留有單一基因副本的酵母基因進(jìn)行處理。美國(guó)威斯康辛大學(xué)麥迪遜分?？茖W(xué)家解釋到,，“我們對(duì)進(jìn)化過(guò)程進(jìn)行還原”。此項(xiàng)研究詳細(xì)演示了古代基因是如何通過(guò)復(fù)制和勞動(dòng)分工提升效率的,。
卡羅爾說(shuō),，“他們?cè)诠ぷ髦胁扇∽罴逊绞健Ｋ麄児采坦ぷ?，共同工作使他們的表現(xiàn)比古代基因的更好,。自然選擇使一個(gè)基因具有兩種功能，創(chuàng)造一個(gè)兩種特定基因的組裝線(xiàn),。”
原文：
A gene divided reveals the details of natural selection
In a molecular tour de force, researchers at the University of Wisconsin-Madison have provided an exquisitely detailed picture of natural selection as it occurs at the genetic level.
Writing today in the journal Nature, Howard Hughes Medical Institute investigator Sean B. Carroll and former UW-Madison graduate student Chris Todd Hittinger document how, over many generations, a single yeast gene divides in two and parses its responsibilities to be a more efficient denizen of its environment. The work illustrates, at the most basic level, the driving force of evolution.
"This is how new capabilities arise and new functions evolve," says Carroll, one of the world's leading evolutionary biologists. "This is what goes on in butterflies and elephants and humans. It is evolution in action."
The work is important because it provides the most fundamental view of how organisms change to better adapt to their environments. It documents the workings of natural selection, the critical idea first posited by Charles Darwin where organisms accumulate random variations, and changes that enhance survival are "selected" by being genetically transmitted to future generations.
The new study replayed a set of genetic changes that occurred in a yeast 100 million or so years ago when a critical gene was duplicated and then divided its nutrient processing responsibilities to better utilize the sugars it depends on for food.
"One source of newness is gene duplication," says Carroll. "When you have two copies of a gene, useful mutations can arise that allow one or both genes to explore new functions while preserving the old function. This phenomenon is going on all the time in every living thing. Many of us are walking around with duplicate genes we're not aware of. They come and go."
In short, says Carroll, two genes can be better than one because redundancy promotes a division of labor. Genes may do more than one thing, and duplication adds a new genetic resource that can share the workload or add new functions. For example, in humans the ability to see color requires different molecular receptors to discriminate between red and green, but both arose from the same vision gene.
The difficulty, he says, in seeing the steps of evolution is that in nature genetic change typically occurs at a snail's pace, with very small increments of change among the chemical base pairs that make up genes accumulating over thousands to millions of years.
To measure such small change requires a model organism like simple brewer's yeast that produces a lot of offspring in a relatively short period of time. Yeast, Carroll argues, are perfect because their reproductive qualities enable study of genetic change at the deepest level and greatest resolution because researchers can produce and quickly count a large number of organisms. The same work in fruit flies, one of biology's most powerful models, would require "a football stadium full of flies" and years of additional work, Carroll explains.
"The process of becoming better occurs in very small steps. When compounded over time, these very small changes make one group of organisms successful and they out-compete others," according to Carroll.
The new study involved swapping out different regions of the yeast genome to assess their effects on the performance of the twin genes, as well as engineering in the gene from another species of yeast that had retained only a single copy.
"We retraced the steps of evolution," the Wisconsin biologist explains.
The work shows in great detail how the ancestral gene gained efficiency through duplication and division of labor.
"They became optimally connected in that job. They're working in cahoots, but together they are better at the job the ancestral gene held," Carroll says. "Natural selection has taken one gene with two functions and sculpted an assembly line with two specialized genes."
