生物学领域 - 高级

What's a domain?
::什么是域名?

.com, .org, .edu are domain names. They can immediately classify a site into a general category. So can the domains , , and Eukayra.
::com, .org, edu是域名。 它们可以立即将网站分类为普通类别。 域名, 和 Eukayra 也可以分类 。

The Domain
::域域

Carl Woese wasn’t completely happy with the six- system. It didn’t show that all four eukaryote kingdoms are more closely related to each other than to the two bacteria kingdoms. It also didn’t show that the two bacteria kingdoms are as different from each other as they are from the eukaryote kingdoms. To show these similarities and differences, Woese introduced a new taxon called the domain . He defined domain as a taxon higher than the kingdom.
::卡尔·沃塞斯对六大体系并不完全满意。 它没有表明四个尤卡里奥特王国都比两个细菌王国更紧密地联系在一起。 它也没有表明这两个细菌王国与乌卡里奥特王国不同。 为了表明这些相似和不同之处,沃塞推出了一个新的称为域名的税种。 他把域定义为比王国更高的税种。

The Three-Domain System
::三域系统

In 1990, Woese and his colleagues proposed a new system containing three domains: Bacteria, Archaea, and Eukarya . As shown in Figure , the Bacteria domain was formerly the Eubacteria kingdom, and the Archaea domain was formerly the Archaebacteria kingdom. The Eukarya domain includes all four eukaryote kingdoms: plants, , , and . The three-domain system emphasizes the similarities among eukaryotes and the differences among eukaryotes, bacteria, and archaea. By using domains, Woese was able to show these relationships without replacing the popular six-kingdom system.
::1990年,Wouse及其同事提出了包含三个领域的新系统:细菌、Archaea和Eukarya。如图所示,细菌领域原为Eubacteria王国,而Archaea领域原为Archaebacteria王国。Eukarya领域包括所有四个eukaryote王国:植物、植物和。三领域制度强调eukaryotes之间的相似性以及eukaryotes、细菌和Archaea的差异。通过使用域,Woese得以展示这些关系,而没有取代流行的六国制。

Archaea were first found in extreme environments. For example, they were found in the hot geysers in Yellowstone National park. Archaea have since been found in all of Earth’s habitats . They are now known to be present everywhere and in high numbers. They may contribute as much as 20 percent to Earth’s total biomass .
::Archaea最初是在极端环境中发现的。 例如,在黄石公园的热壁炉中发现了Archaea。 Archaea后来在所有地球栖息地中都发现了Archaea。现在,众所周知,他们无处不在,数量众多。 他们可能占地球总生物量的20%。

Woese’s three-domain system was quickly adopted by many other biologists. There were some critics, however, who argued that the system put too much emphasis on the uniqueness of Archaea. Later studies confirmed how different Archaea are from other organisms . For example, organisms belogning to Archaea were found to differ from both Eukarya and Bacteria in the composition of their and the system they use for DNA replication . These differences convinced most critics that the three-domain system was justified. After its introduction in 1990, the three-domain system became increasingly popular. Within a decade of its introduction, it had largely replaced earlier classifications.
::许多其他生物学家很快采用了Weses的三域系统。 但是,有些批评家认为这个系统过于强调Archaea的独特性。 后来的研究证实了Archaea与其他生物的区别。 比如,发现向Archaea传入Archaea的生物与Eukarya和细菌的构成及其用于DNA复制的系统不同。 这些差异让大多数批评家相信,三域系统是有道理的。 在1990年引入后,三域系统越来越受欢迎。 在引进后十年内,它基本上取代了以前的分类。

How Are the Three Domains Related?
::三域关系如何?

Comparing ribosomal RNA base sequences, Woese and his colleagues also showed that organisms belonging to Eukarya are more similar to Archaea than they are to Bacteria. Figure is a phylogenetic tree based on their analysis. This tree places Archaea and Eukarya in the same clade . It represents the hypothesis that Archaea and Eukarya shared a more recent common ancestor with each other than either shared with Bacteria.
::Woese和他的同事在比较 RNA 基准序列时还表明,属于Eukarya 的生物比属于Archaea 的生物更类似于Archaea。根据分析,图是植物基因树。这棵树将Archaea 和 Eukarya 放在同一片板条上。它代表了一种假设,即Archaea 和 Eukarya 彼此拥有一个较新的共同祖先,而不是与细菌共享。

The results of a study published in 2007 seem to conflict with this hypothesis. Comparing base sequences, the 2007 study suggested that the domain Archaea may be older than either Bacteria or Eukarya. That would make Archaea the most ancient group of organisms on Earth. It is not yet known, which, if either, hypothesis is correct. Scientists need to learn more about Archaea and their relationships with other organisms to resolve these questions.
::2007年公布的一项研究结果似乎与这一假设相冲突。 比较基准序列,2007年研究表明,Archaea领域可能比细菌或Eukarya年长。这将使Archaea成为地球上最古老的生物群体。 尚不清楚,如果假设正确的话,假设是正确的。 科学家们需要更多地了解Archaea及其与其他生物的关系,才能解决这些问题。

The Future of Classification
::分类的未来

The three-domain system is unlikely to be the final word on classification. The system is based on the current state of knowledge. As knowledge increases, the three-domain system may need revision. For example, the number of domains may change as scientists learn more about those life forms we currently know little about.
::三域系统不太可能是分类的最后词。 系统基于当前知识状况。 随着知识的增加,三域系统可能需要修改。 例如, 随着科学家更多地了解我们目前所知不多的生命形式, 领域的数量可能会发生变化 。

A recent discovery illustrates this point. In 2003, scientists identified a new called mimivirus. It resembles bacteria in size and number of genes . However, the virus cannot respond to stimuli or grow by , both of which are traits of bacteria and other living organisms. Mimivirus’ unique combination of traits seems to place it at the boundary between living and nonliving things. Some scientists think mimivirus might represent a new domain of life.
::最近的发现说明了这一点。 2003年,科学家们发现了一种新的叫咪咪病毒。它与基因大小和数量的细菌相似。然而,病毒无法对刺激性反应或生长,而两者都是细菌和其他活生物体的特征。 咪咪病毒的独特特征组合似乎将它置于生物和非生物的界限。 一些科学家认为咪咪病毒可能代表一个新的生命领域。

Summary
::摘要

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• In 1990, the three-domain system was introduced and is now the most widely used classification system. The three domains are Bacteria, Archaea, and Eukarya.
  ::1990年,引进了三域系统,现已成为最广泛使用的分类系统,其中三个领域是细菌、Archaea和Eukarya。
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• As knowledge of organisms increases in the future, the three-domain system may need revision. For example, new domains may need to be added.
  ::随着未来对生物体的了解增加,三域系统可能需要修订,例如,可能需要增加新的领域。

Review
::回顾

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1. What is a domain?
   ::什么是域名?
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2. Explain in which domain you would classify an organism that consists of a single cell with a nucleus.
   ::解释您要在哪个区域分类一个有机体, 它由带有核的单细胞组成 。
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3. Compare and contrast Bacteria, Archaea, and Eukarya.
   ::对比和对比细菌,Archaea和Eukarya。
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4. What problem with the six-kingdom classification system was addressed by the three-domain classification system? How did it address the problem?
   ::三域分类制度解决了六国分类制度有什么问题?如何解决这个问题?
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5. Describe the relationship between the original bacteria kingdom called monera and the domain called bacteria.
   ::描述原始细菌王国与细菌之间的关系。