託福閱讀TPO31(試題+答案+譯文)第1篇:SpeciationinGeographicallyIsolatedPop
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託福閱讀原文
【1】Evolutionary biologists believe that speciation, the formation of a new species, often begins when some kind of physical barrier arises and divides a population of a single species into separate subpopulations. Physical separation between subpopulations promotes the formation of new species because once the members of one subpopulation can no longer mate with members of another subpopulation, they cannot exchange variant genes that arise in one of the subpopulations. In the absences of gene flow between the subpopulations, genetic differences between the groups begin to accumulate. Eventually the subpopulations become so genetically distinct that they cannot interbreed even if the physical barriers between them were removed. At this point the subpopulations have evolved into distinct species. This route to speciation is known as allopatry (“alio-” means “different”，and “patria” means “homeland”).
【2】Allopatric speciation may be the main speciation route. This should not be surprising, since allopatry is pretty common. In general, the subpopulations of most species are separated from each other by some measurable distance. So even under normal situations the gene flow among the subpopulations is more of an intermittent trickle than a steady stream. In addition, barriers can rapidly arise and shut off the trickle. For example, in the 1800s a monstrous earthquake changed the course of the Mississippi River, a large river flowing in the central part of the United States of America. The change separated populations of insects now living along opposite shore, completely cutting off gene flow between them.
【3】Geographic isolation also can proceed slowly, over great spans of time. We find evidence of such extended events in the fossil record, which affords glimpses into the breakup of formerly continuous environments. For example, during past ice ages, glaciers advanced down through North America and Europe and gradually cut off parts of populations from one another. When the glacier retreated, the separated populations of plants and animals came into contact again. Some groups that had descended from the same parent population were no longer reproductively compatible—they had evolved into separate species. In other groups, however, genetic divergences had not proceeded so far, and the descendants could still interbreed—for them, reproductive isolation was not completed, and so speciation had not occurred.
【4】Allopatric speciation can also be brought by the imperceptibly slow but colossal movements of the tectonic plates that make up Earth’s surface. About 5 million years ago such geologic movements created the land bridge between North America and South America that we call the Isthmus of Panama. The formation of the isthmus had important consequences for global patterns of ocean water flow. While previously the gap between the continents had allowed a free flow of water, now the isthmus presented a barrier that divided the Atlantic Ocean from the Pacific Ocean. This division set the stage for allopatric speciation among populations of fishes and other marine species.
【5】In the 1980s, John Graves studied two populations of closely related fishes, one population from the Atlantic side of isthmus, the other from the Pacific side. He compared four enzymes found in the muscles of each population. Graves found that all four Pacific enzymes function better at lower temperatures than the four Atlantic versions of the same enzymes. This is significant because Pacific seawater is typically 2 to 3 degrees cooler than seawater on the Atlantic side of isthmus. Analysis by gel electrophoresis revealed slight differences in amino acid sequence of the enzymes of two of the four pairs. This is significant because the amino acid sequence of an enzyme is determined by genes.
【6】Graves drew two conclusions from these observations. First, at least some of the observed differences between the enzymes of the Atlantic and Pacific fish populations were not random but were the result of evolutionary adaption. Second, it appears that closely related populations of fishes on both sides of the isthmus are starting to genetically diverge from each other. Because Graves’s study of geographically isolated populations of isthmus fishes offers a glimpse of the beginning of a process of gradual accumulation of mutations that are neutral or adaptive, divergences here might be evidence of allopatric speciation in process.
託福閱讀試題
1.The word "promotes" in the passage is closest in meaning to
A.describes.
B.encourages.
C.delays.
D.requires.
2.According to paragraph 1, allopatric speciation involves which of the following?
A.The division of a population into subspecies.
B.The reuniting of separated populations after they have become distinct species.
C.The movement of a population to a new homeland.
D.The absence of gene flow between subpopulations.
3.Why does the author provide the information that "the subpopulations of most species are separated from each other by some measurable distance"?
A.To indicate how scientists are able to determine whether subpopulations of a species are allopatric.
B.To define what it means for a group of animals or plants to be a subpopulation.
C.To suggest that allopatric speciation is not the only route to subpopulation.
D.To help explain why allopatric speciation is a common way for new species to come about.
4.The word "accumulate" in the passage is closest in meaning to
A.Become more significant.
B.Occur randomly.
C.Gradually increase in number.
D.Cause changes.
5.In paragraph 2,why does the author mention that some insect populations were separated from each other by a change in the course of Mississippi River caused by an earthquake?
A.To make the point that some kind of physical barrier separates the subpopulations of most species.
B.To support the claim that the condition of allopatry can sometimes arise in a short time.
C.To provide an example of a situation in which gene flow among the subpopulations of a species happens at a slow rate.
D.To explain why insects living along opposite shores of the Mississippi River are very different from each other.
6.According to paragraph 3，separation of subpopulations by glaciers resulted in speciation in those groups of plants and animals that
A.were reproductively isolated even after the glaciers disappeared.
B.had adjusted to the old conditions caused by the glaciers.
C.were able to survive being separated from their parent population.
D.had experienced some genetic divergences from their parent population.
7.The word "colossal" in the passage is closet in meaning to
A.consistent.
B.gradual.
C.enormous.
D.effective.
8.According to paragraph 4, which of the following is true of the geologic movements that brought about the Isthmus of Panama?
A.The movements brought populations of certain fishes and marine organisms into contact with one another for the first time.
B.The movements transferred populations of fishes and other marine animals between the Pacific and Atlantic Oceans.
C.The movements created conditions that allowed water to flow more freely between the Pacific and Atlantic Oceans.
D.The movements created conditions for the formation of new species of fishes and other marine animals.
9.The word "sequence" in the passage is closet in meaning to
A.quality.
B.order.
C.function.
D.number.
10.According to paragraph 5, by comparing the enzymes from two related groups of fishes on opposite sides of the isthmus, Graves found evidence that
A.there were slight genetic divergences between the two groups.
B.the Atlantic group of fishes were descended from the Pacific group of fishes.
C.the temperature of water on either side of the isthmus had changed.
D.genetic changes in the Atlantic group of fishes were more rapid and frequent than in the Pacific group of fishes.
11.It can be inferred from paragraph 5 and 6 that the reason Graves concluded that some of the differences between the Pacific and Atlantic enzymes were not random was that
A.each of the Pacific enzymes works better in cooler waters.
B.the Enzymes of the Atlantic fish populations had not changed since the formation of the Isthmus of Panama.
C.gel electrophoresis showed that the changes benefited both the Atlantic and the Pacific fish populations.
D.the differences between the enzymes disappeared when the two fish populations were experimentally switched to other side of the isthmus.
12.Which of the sentence below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
A.Graves's study provides evidence that isthmus fishes are in the process of becoming geographically isolated.
B.Graves's study of mutating isthmus fishes yields results that differ from results of other studies involving allopatric speciation.
C.Graves's study of isolated populations of isthmus fishes provides some evidence that allopatric speciation might be beginning
D.Grave's study indicates that when isolated, populations of isthmus fished register neutral or adaptive mutations.
13. Look at the four squares [■] that indicate where the following sentence can be added to the passage.Where would the sentence best fit? The formation of the isthmus had important consequences for global patterns of ocean water flow.
Allopatric speciation can also be brought by the imperceptibly slow but colossal movements of the tectonic plates that make up Earth's surface. ■【A】 About 5 million years ago such geologic movements created the land bridge between North America and South America that we call the Isthmus of Panama. The formation of the isthmus had important consequences for global patterns of ocean water flow. ■【B】 While previously the gap between the continents had allowed a free flow of water, now the isthmus presented a barrier that divided the Atlantic Ocean from the Pacific Ocean. ■【C】This division set the stage for allopatric speciation among populations of fishes and other marine species. ■【D】
14. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passages or are minor ideas in the passage. This question is worth 2 points.
Allopatric speciation takes place when physically separated populations of a single species gradually diverge genetically to the point of becoming unable to interbreed
A.Allopatric speciation is common because the gene flow between subpopulations is generally limited and the barriers that completely separate subpopulations can arise in a variety of ways.
B.During past ice ages, some, but not all, subpopulations separated by glaciers evolved into distinct species.
C.Speciation does not need to take place through allopatry because subpopulations will form distinct species whenever there are adaptive advantages or not
D.Physical barriers from glaciers and the movement of tectonic plates form so slowly that the subpopulations on either side of the barriers usually do not form distinct species.
E.Graves's study of fish populations separated by the Isthmus of Panama may well provide a picture of the beginning stages of speciation.
F.Graves's study of physically separated fish populations show that there must be large differences between the environments of the isolated populations if allopatric speciation is to take place.
託福閱讀答案
1.promote本身是促進的意思。另外原文這個句子意思是subpopulations間的物理分割...了新物種的形成，A描 述，B促使，C減弱，D要求。 所以B最合適的。
2.根據allopatric進行定位，可定位至本段的最後一句。最後一句是對前面現象的一個命名和定義。也就是說前 面的內容，就是allopatry的意 思。A與原文不附，原文說的 是物理 barrier 把 population 分割成 subpopulation，B 也不對， 對應Eventually這句。C原文沒提到。D正確，對應從In the absence開始到最後。
3.高亮句前面的一句話，也就是本段的第一句(主旨句)，allopatry是main speciation route。本段都是圍繞着這個主題來進行的。所以選擇D。
4.詞彙所在句說羣落間基因的區別開始accumulate。 Eventually對理解這個詞很有 幫助，也就是說是漸漸發展的，才能說最終。所以答案在A，C之間。但因爲這裏強調了緩慢的過 程，gradually更合適。
5.For example後面就是題目中的內容，那麼也就是說作者用此作爲例子來支持前 面的觀點。而前面的觀點是 barriers也有可能突然發生，然後截斷了這種trickle。所以對應的是B。
6.根據Glaciers 和 plants and animals定位，可得知這是glacier separation 導致的結果。所以對應選項A。
7.Colossal本身是巨大的， 非常的意思，這裏對應C選項。分析原文也可以得到正確答案，與colossal並列的詞彙是slow，中間的邏輯關係詞 是but,證明兩者有轉折關係。再經過推斷，緩慢的過程但量 大的話就足以發生巨大的改變。所以選C。
8.根據 Isthmus of Panama 定位。從About開始。本段的 最後一句說了isthmus of Panama帶來的結果，對應了D選項。
9.高亮詞所在句提到了氨基酸，酶，pairs這些話題，其實就是在說成對的基因，膠體電泳分析揭示了少量的氨基酸的不同。A質量，C 功能，D數量都不對，應該選擇B順序。
10.跟上面一題對應的位置是一樣的。或者可以根據Graves found定位，閱讀後面的部分可得出答案A。
11.A對應了標註句子，B明顯錯誤，文章一直在說改變。C文章提到 gel electrophoresis的地方只是說氨基酸的順序改變，但沒說both benefited。D文章也沒提到。
12.原文高亮句翻譯爲：格雷夫斯關於地峽魚類地域隔離的種羣研究爲中性或適應性突變的逐漸累積過程的開始提供了一些線索，這裏的差異可能會給正在進行的異域性物種的形成提供證據。所以主幹部分爲...的研究爲..的開始提供了線索，對應C。
13.要插入的句子提到了 formation of the isthmus，那麼證明句子前面的內容中己經出現了isthmus，而後面則是 要說明consequences。第二個空符合邏輯，所以選擇B。
14.ABE
託福閱讀譯文
【1】進化生物學家認爲物種形成(也就是新物種的產生)經常是某種物理障礙(地理隔離)的出現把一個單一物種羣分爲隔離的亞種羣。亞種羣的身體隔離促進了新物種的產生，因爲一旦亞種羣中的成員無法與其他亞種羣中的成員交配，那麼亞種羣之間就沒有變種基因的交換。缺乏了基因交流，亞種羣之間的遺傳差異就開始變大。最終這些亞種羣的基因差異變得十分明顯，以至於它們無法進行種族內的交配，即使它們之間的物理障礙已經消除。這時，這些亞種族就演化成了獨立的物種。這樣的物種形成的方式被稱作異域性(“alio-”意思是“不同的”,“patria”意爲“故鄉”)。
【2】異域性物種形成可能是最主要的物種形成方式。這沒什麼驚訝的，因爲異域現象太常見。一般而言，大多數的物種的亞種族都是被遙遠距離所隔開，所以即使在正常條件下，這些亞物種間的基因流動倒更像是一條斷斷續續的細流，而不是一條不停流淌的小溪。並且，障礙也會迅速出現來截斷這條細流。例如，19世紀的一次大地震改變了密西西比河(美國中部的一條大河)的流向，這個變化使得當地的昆蟲分離開來，它們現在居住於河的兩岸，彼此的基因流動已被完全截斷。
【3】地理隔離也能緩慢地進行，會跨越很長的時間段。我們在化石記錄中找到了這種長期證據，從中我們可以瞥見先前延續環境的破碎。比如說，在過去的冰河世紀，經過北美和歐洲的冰川最終把種羣的部分彼此切斷，當冰川消退後，這些分離的動植物種羣又會連到一起。一些起源於同一母羣的羣體變得不再那麼容易兼容——它們演化成了分開的物種。然而，在另一些羣體裏，遺傳差異並沒有那麼明顯，後代們還是可以種族內互相交配的繁殖，隔離並沒有徹底，所以物種形成就沒有發生。
【4】異域性物種的形成也可能是由構成地球表面的地殼構造板塊運動所產生的，這個運動雖略微緩慢但卻異常劇烈。大約五百萬年前這種地質運動形成了連接北美和南美的大陸橋，也就是我們今天所說的巴拿馬地峽。巴拿馬地峽的形成對全球洋流的模式產生了重大的影響。之前，大陸間的這個缺口可以讓水自由流動，而現在巴拿馬地峽在大西洋和太平洋之間形成了一道屏障。這個地域分割爲魚和其他海洋物種的異域性物種形成創造了條件。
【5】20世紀80年代，約翰??格雷夫斯研究了兩個緊密相關的魚種，一種來自地峽的大西洋一側，另一種來自太平洋那一側。他比較了每個魚種肌肉裏的四種酶。格雷夫斯發現在低溫條件下，位於太平洋一側的魚種裏的全部四類酶比大西洋一側的四種酶功能更好。這個發現很重要，因爲太平洋的海水的水溫通常要比地峽另一側大西洋的海水低2到3度。凝膠電泳的分析顯示，四對中的兩對酶的氨基酸序列略有不同。這也很重要，因爲酶的氨基酸序列是由基因決定的。
【6】根據這些觀測，格雷夫斯得出了兩個結論。第一，在這些觀測到的大西洋和太平洋魚種體內酶的差異中，至少有一些不是偶然的，它們是適應進化的結果。第二，似乎地峽兩側原 本密切相關的魚種開始有了基因分化。因爲格雷夫斯關於地峽魚類地域隔離的種羣研究爲中性或適應性突變的逐漸累積過程的開始提供了一些線索。這裏的差異可能會給正在進行的異域性物種的形成提供證據。
託福閱讀TPO31(試題+答案+譯文)第1篇:Speciation in Geographically Isolated Populations
