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  • Cladistics - 高级

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    Are these related?
    ::这些是相关的吗?

    They are. But which two fish are more closely related than others? Understanding how these fish are related would take the work of an evolutionary biologist. The generation of a cladogram would demonstrate the relatedness of these species.
    ::它们是。 但哪两条鱼类比其他鱼类更紧密地联系在一起? 了解这些鱼类是如何联系在一起的,这需要进化生物学家的工作。 单形图的生成将显示这些物种的关联性。

    Cladistics and Classification
    ::克拉底和分类

    The most common method of incorporating information into phylogenetic trees is called cladistics . Cladistics depict hypotheses about how organisms are related based on traits of ancestor and descendent species. The use of Cladistics was developed in the 1950s by a scientist named Willi Hennig. Over the next several decades, it became very popular and is still widely used today.
    ::将信息纳入植物基因树中最常用的方法叫“单词” 。 单词描述基于祖先和后代物种特征的生物关系假设。 1950年代,一位名叫Willi Hennig的科学家开发了使用单词。 在未来几十年里,它变得非常受欢迎,今天仍然被广泛使用。

    Clades and Cladograms
    ::晶片和晶晶图

    The term cladistics comes from the word clade . A clade is a group of organisms that includes an ancestor species and all of its descendants. A diagram showing evolutionary relationships within one or more clades is called a cladogram . A clade is a relative concept. How you define a clade depends on which species you are interested in classifying. Small clades can include as few as two species and their common ancestor. The larger clades can include many more species and their common ancestors.
    ::单字词来自 clade 。 缩写是一组有机体, 包括一个祖先物种及其后代。 显示一个或一个以上圆环内进化关系的图表叫做单形图。 缩写是一个相对的概念。 您如何定义一个缩写, 取决于您对分类感兴趣的物种。 小缩写可以包括两个不同的物种及其共同祖先。 大缩写可以包括更多的物种及其共同祖先。

    As another example, consider the cladogram of insect phylogeny shown in the Figure  . According to this cladogram, beetles were the first insect to branch off from a common ancestor. Then, the group that includes wasps, bees, and ants branched off. Finally, flies branched off from their common ancestor with butterflies and moths. All can be considered a clade because they have a common ancestor. Butterflies, moths, and flies can also be considered a clade for the same reason. Can you identify other clades in the Figure  ? For example, can you find the clade of all non-beetle insects?
    ::举另一个例子, 想想图中显示的昆虫植物的单形形形图。 根据这个单形图, 甲虫是第一个从共同祖先处切开的昆虫。 然后, 包括黄蜂、 蜜蜂和蚂蚁在内的群。 最后, 用蝴蝶和飞蛾从它们共同的祖先处开来。 所有这些都可以被看作一块刀片, 因为它们有一个共同的祖先。 蝴蝶、 蛾类和苍蝇也可以被同样的理由视为一块刀片。 您能否在图中找到其他的单形? 比如, 您能找到所有非虫昆虫的刀片吗 ?

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    Cladogram of Insect Phylogeny. Based on this cladogram, flies shared a more recent common ancestor with butterflies and moths than either group shared with other insects. What other evolutionary relationships does the cladogram reveal?

    Generating Cladograms
    ::正在生成克拉格

    How do scientists construct cladograms like the one in the Figure  ? The starting point is a set of data on traits of a group of related species. The traits could be physical traits, genetic traits, or both (see Evidence for Evolutionary Relationships below). The next step is deciding which traits were inherited from the common ancestor and which traits evolved only in a descendant species after splitting off from the common ancestor. Traits inherited from a common ancestor are called ancestral traits . Traits that evolved since two groups shared a common ancestor are called derived traits , and both types of traits are illustrated in the Figure  .
    ::科学家如何构建像图中那样的单形图?起点是一组有关物种特征的数据。这些特征可以是物理特征、遗传特征,也可以是两者兼而有之(见下文关于进化关系的证据)。下一步是决定哪些特征是从共同祖先继承的,哪些特征在与共同祖先分离后仅从后代物种中演变而来。从共同祖先继承的遗产被称为祖传特征。自两个群体共同祖先被称作衍生特征而演变而来,两种特征在图中都有说明。

    Ancestral and Derived Traits in Cladistic Analysis
    ::克拉底分析中的祖传和衍生轨迹

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    In this cladogram, the ancestor species has traits A, B, and C, so these are ancestral traits. During the process of evolution, trait A evolves to trait a and trait B evolves to trait b. These new traits (a and b) are derived traits. Organisms can be classified into separate groups (species #1 or species #2) on the basis of these derived traits.

    Consider as an example. A derived trait in birds is feathers . The trait is present only in birds and was not inherited from a common ancestor of birds and other organisms. An example of an ancestral trait in birds is the presence of . Eyes are present not only in birds but also in many other groups of that share a common ancestor with birds. Therefore, the presence of feathers can identify an organism as a bird, but the presence of eyes cannot. In cladistics, the sharing of derived traits is the most important evidence for evolutionary relationships. Organisms with the same derived traits (such as feathers) are grouped in the same clade.
    ::以鸟类为例。鸟类的一个衍生特征是羽毛。这种特征只存在于鸟类身上,并非从鸟类和其他生物的共同祖先继承而来。鸟类的一个祖传特征例子是鸟类的存在。眼睛不仅存在于鸟类中,而且存在于与鸟类有共同祖先的许多其他群体中。因此,羽毛的存在可以将有机体确定为鸟类,但眼睛无法存在。在单词中,分享衍生特征是进化关系的最重要证据。具有相同衍生特征(如羽毛)的有机体被分组在同一块板上。

    A derived trait is not necessarily an entirely new trait. More often it is a modified form of an ancestral trait. For example, birds evolved feathers from the scales that were already present in their ancestor. Similarly, mammals evolved fur from the scales of their reptilian ancestors.
    ::衍生的特性并不一定是全新的特性,更经常地是古代特性的变异形式。 比如,鸟类从已经存在于其祖先中的天平上进化羽毛。 同样,哺乳动物从其爬行动物祖先的天平上进化毛皮。

    More than one possible cladogram can usually be created from the same set of data. In fact, the number of possible cladograms increases exponentially with the number of species included in the analysis. Only one cladogram is possible with two species. More than 100 cladograms are possible with five species. With nine species, more than two million cladograms are possible! The Figure  shows just six of the many possible cladograms that can be generated for five species.
    ::通常可以通过同一组数据生成一个以上可能的单方形。 事实上, 可能的单方形数量随分析中包括的物种数量而成倍增长。 只有两个物种可以生成一个单方形。 五个物种可以生成100多个单方形。 有九个物种, 可能生成200多万单方形。 图仅显示五个物种可能产生的许多单方形中的六个。

    Six Possible Cladograms for Five Hypothetical Species
    ::五个假设物种的六种可能的晶形图

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    The same set of data on five related species may generate over 100 possible cladograms. Just six are shown here. In cladogram 1 (top, left), D and E share a more recent common ancestor than either shares with C. In cladogram 2 (top, middle), C and D share a more recent common ancestor than either shares with E. Compare how each of the remaining cladograms differs from the others.

    Choosing the Best Cladogram
    ::选择最佳克拉立方图

    How do scientists know which of many possible cladograms is the “right” one? There is no right or wrong cladogram. However, some cladograms fit the facts better than others. Statistical methods can be used to determine which cladogram best fits a particular data set. An important deciding factor is parsimony. Parsimony means choosing the simplest explanation from among all possible explanations. In cladistics, parsimony usually means choosing the cladogram with the fewest branching points.
    ::科学家如何知道“ 正确” 的单张图中哪些是“ 正确” 的单张图? 没有对错的单张图。 但是, 有些单张图比其他单张图更适合事实。 统计方法可以用来确定哪个单张图最适合特定数据集。 一个重要的决定因素是 palsimony 。 Parsimony 意味着从所有可能的解释中选择最简单的解释。 在单张图中, 单张通常意味着以最小的分支点选择单张图 。

    A cladogram shows just one of many possible phylogenies for a group of organisms. It can provide insights into how evolution occurred. However, a cladogram should not be considered a model of actual evolutionary events. It does not necessarily show what really happened. It just shows what could have happened.
    ::单方形图只显示一组生物的许多可能的血源之一。 它可以提供对进化过程的洞察力。 但是, 单方形图不应被视为实际进化事件的模型。 它不一定能显示实际发生的事情。 它只是显示可能发生的事情 。

    Phylogenetic Classification
    ::生代遗传学分类

    A cladogram shows how species may be related by descent from a common ancestor. A of organisms on the basis of such relationships is called a phylogenetic classification . A phylogenetic classification involves placing organisms in a clade with their common ancestor. Consider the cladogram in the Figure  . It groups birds in the same clade as reptiles, because a variety of evidence suggests that birds evolved from a reptilian ancestor. The cladogram places mammals in a separate clade, because evidence suggests that mammals evolved from a different ancestor.
    ::单方形图显示物种如何可能与来自共同祖先的血统有关。基于这种关系的有机体的A类被称作植物基因分类。一种植物基因分类涉及将生物与共同祖先放在一块刀片上。在图中考虑单方形图。它将鸟类与爬行动物放在一块刀片上,因为有各种证据表明鸟类从爬行动物祖先演变而来。单方形图将哺乳动物放在一块单独的刀片上,因为有证据表明哺乳动物是从不同的祖先演变而来的。

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    This cladogram represents the evolutionary history of reptiles, birds, and mammals. The reptile clade includes birds. Mammals are in a separate clade.

    Figure  shows the phylogenetic classification of reptiles, birds, and mammals based on the cladogram in Figure . Birds are grouped with reptiles in one clade, called the Sauropsids . Mammals and their reptile-like ancestor are grouped in a separate clade, called the Synapsids. Compare this phylogenetic classification with the Linnaean classification , also shown in Figure  . In the Linnaean classification, reptiles, birds, and mammals are all placed in separate classes based on differences in physical traits. This classification artificially separates both birds and mammals from their reptilian ancestors. It also illustrates the difficulty of showing evolutionary relationships with Linnaean taxonomy .
    ::图中显示了根据图中的单形图对爬行动物、鸟类和哺乳动物进行植物遗传分类的情况。鸟类与爬行动物分组,在一个称为“Sauropsids”的刀片中。哺乳动物及其类似爬行动物的祖先被单独分组,在一个称为“Synapsids”的刀片中。将这种植物遗传分类与“Linnae”的分类相比较,也在图中显示。在林奈人分类中,爬行动物、鸟类和哺乳动物都根据物理特征的不同而分别分类。这种分类将鸟类和哺乳动物与他们的爬行动物祖先人为地区分开来。它也说明了显示与林奈人分类的进化关系的难度。

    Phylogenetic and Linnaean Classifications of Reptiles, Birds, and Mammals
    ::爬虫、鸟类和哺乳动物的基因遗传和林内人分类

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    The cladistic classification on the right assumes that mammals and birds evolved from different reptilian ancestors. Mammals are placed in one clade, and birds are placed in another clade (with modern reptiles). Compare this classification with the Linnaean classification on the left. Why are birds and reptiles placed in separate classes in the Linnean taxonomy?

    Both phylogenetic and Linnaean classification systems have advantages and drawbacks (see the point by point comparison in the two lists, below). As an overall approach, most biologists think that phylogenetic classification is preferable to Linnaean classification. This is because it is based on evolutionary relationships and not just similarities in physical traits that may or may not have evolutionary significance. However, both approaches have a place in the classification of organisms. Linnaean binomial names are still needed to identify species, because phylogenetics does not include a method for naming species. In addition, many higher taxa in the Linnaean system, such as birds and mammals, remain useful in phylogenetic classifications. This is because they are also clades.
    ::植物基因分类制度和林内人分类制度都有优点和缺点(见下文两个清单中的点对点比较)。作为一个总体方法,大多数生物学家认为,植物基因分类比林内人分类更可取,因为其基础是进化关系,而不只是可能具有进化意义或可能不具进化意义的物理特征的相似性。但是,这两种方法在生物分类中都有其位置。林内人二进制名称对于确定物种仍然有必要,因为植物学并不包括命名物种的方法。此外,林内人系统中许多更高的分类群,例如鸟类和哺乳动物,在植物遗传分类中仍然有用。这是因为它们也是晶体。

    Phylogenetic Classification
    ::生代遗传学分类
    1. Treats all levels of a cladogram as equivalent.
      ::单声图的所有级别均作为等值处理。
    2. Places no limit on the number of levels in a cladogram.
      ::对单方图中的级别数没有限制。
    3. The primary goal is to show the process of evolution.
      ::首要目标是展示进化过程。
    4. It is limited to organisms that are related by ancestry.
      ::它仅限于与祖先相关的生物。
    5. Does not include a method for naming species.
      ::不包括命名物种的方法。
    Linnaean Classification
    ::林内人分类
    1. Treats each taxa uniquely and has a special name for each (e.g., genus , species).
      ::每个分类群都有独特的待遇,每个分类群都有特殊的名称(例如,基因、物种)。
    2. Has fixed numbers and types of taxa.
      ::具有固定数目和类型的分类群。
    3. Primary goal is to group species based on similarities in physical traits.
      ::首要目标是根据生理特征的相似性对物种进行分类。
    4. Can include any organism without regard to ancestry.
      ::可包括任何生物,而不考虑祖先。
    5. Has a method for giving unique names to species.
      ::拥有一种给物种提供独特名称的方法。

    Phenetics is an older method to classify organisms. Phenetics is based on overall similarity, usually in morphology or other observable traits, regardless of their evolutionary relation. Phenetics has largely been replaced by cladistics for research into evolutionary relationships among species. Phenetic techniques include various forms of clustering and ordination of traits. These are sophisticated ways of reducing the variation displayed by organisms to a manageable level. Phenetic analyses do not distinguish between traits that are inherited from an ancestor and traits that evolved anew in one or several lineages. Consequently, phenetic analyses can be misled by convergent evolution and adaptive radiation .
    ::化学基于总体相似性,通常是形态学或其他可观察到的特性,而不论其进化关系如何; 化学基本上被用于研究物种间进化关系的单体体学所取代; 遗传技术包括各种特性的组合和调控形式; 这些是将生物所显示的变异降低到可控水平的尖端方法; 理论分析没有区分从祖先继承下来的特性和在一种或几种直系中重新演变的特性; 因此,同系物学分析可能会被趋同进化和适应性辐射所误导。

    Evidence for Evolutionary Relationships
    ::演变关系的证据

    Traditionally, evidence for evolutionary relationships included similarities in physical traits of form or function. For example, in Linnaean taxonomy, homeothermy (warm-bloodedness) is one of the traits used to separate both birds and mammals from other animals (see  Figure ). However, this trait is not suitable for showing evolutionary relationships between birds and mammals. This is because birds and mammals did not inherit the trait of homeothermy from a common ancestor. Both groups independently evolved the trait. The presence of homeothermy in both birds and mammals is an example of convergent evolution (see the concepts). In general, convergent evolution may make two groups seem to be more closely related than they really are. Using such traits for phylogenetic analysis can create misleading phylogenetic classifications.
    ::传统上,进化关系的证据包括形式或功能的物理特征的相似性。例如,在林奈人分类学中,家庭对流(温血)是用来将鸟类和哺乳动物与其他动物区分开来的一种特征(见图 )。但是,这种特征不适合显示鸟类和哺乳动物之间的进化关系,这是因为鸟类和哺乳动物没有继承共同祖先的家庭对流的特征。这两个群体都独立地演变了该特征。鸟类和哺乳动物的家庭对流(家庭对流)的存在是趋同进化的一个例子(见概念 ) 。一般来说,趋同的进化可能使两个群体似乎比它们实际存在的关系更为密切。利用这些特征进行植物遗传学分析可以产生误导性植物遗传学的分类。

    Similarities among base sequences provide some of the most direct evidence of evolutionary relationships (see the Evolution concepts). Nucleic acids directly control genetic traits and copies of nucleic acids are actually passed from parents to offspring. Therefore, similarities in these traits are likely to reflect shared ancestry. By the 1960s, scientists had found ways to sequence the bases in nucleic acids. This coincided with the growing popularity of cladistics. In cladistic analysis, similar nucleic acid base sequences are assumed to indicate descent from a common ancestor. The more similar the sequences, the more recently two groups are assumed to have shared a common ancestor.
    ::核酸直接控制遗传特性和核酸的复制件实际上由父母传给后代。因此,这些特性的相似性可能反映共同的祖先。到1960年代,科学家已经找到方法对核酸的基数进行排序。这与单声带越来越受欢迎的时间吻合。在单声带分析中,类似的核酸基数序列被假定为从共同的祖先中下降。相近的序列中,最近的两个组被假定为共有的祖先。

    Many base sequence comparisons have confirmed genetic relationships that were assumed on the basis of similarities in physical traits. For example, 96 percent of the in humans and chimpanzees is the same. This agrees, in general, with the Linnaean classification of chimpanzees as close human relatives.
    ::许多基准序列比较都证实了遗传关系,而遗传关系是根据生理特征相似性假设的。 比如,人类和黑猩猩中96%的基因和黑猩猩是相同的。 一般来说,这与黑猩猩作为人类近亲的里奈人分类一致。

    Most biologists interested in taxonomy now use nucleic acid sequences or other related molecular data to classify organisms. However, using nucleic acid base sequences for phylogenetic analysis is not without its drawbacks. Two of the drawbacks are the following:
    ::大多数对分类法感兴趣的生物学家现在都使用核酸序列或其他相关的分子数据对生物进行分类,然而,使用核酸基序列进行植物基因分析并非没有缺点。

    • Data on nucleic acids can rarely be obtained for extinct species. This is true even for species represented by . Fossil DNA and generally are not sufficient in quantity or quality to be useful for such analyses.
      ::已经灭绝的物种很少能获得关于核酸的数据,即使是以.Fosil DNA为代表的物种也是如此,通常在数量和质量上都不足以进行这种分析。
    • Base sequence data may be influenced by horizontal gene transfer. This occurs when an organism passes DNA to an unrelated organism. First discovered in in 1959, it is now known to be common in bacteria and some other microorganisms. Horizontal gene transfer can make species seem more closely related than they really are.
      ::基准序列数据可能受横向基因转移的影响。 当生物体将DNA传递给无关生物时,就会发生这种情况。 1959年首次发现,现在在细菌和其他一些微生物中已经很常见。 横向基因转移可以让物种看起来比实际的更紧密地联系在一起。

    Because of horizontal gene transfer, some biologists have started to question whether phylogenetic trees are the best way to show evolutionary relationships. This is especially true for those biologists that are interested in classifying bacteria. An entirely new process of determining evolutionary relationships may be needed in order to include horizontal gene transfer.
    ::由于横向基因转移,一些生物学家开始质疑植物基因树是否是显示进化关系的最好方法。 对那些有兴趣对细菌进行分类的生物学家来说尤其如此。 为了包括横向基因转移,可能需要一个全新的确定进化关系的过程。

    Summary
    ::摘要

    • Cladistics is the most widely used method of generating phylogenetic trees. It is based on evolutionary ancestry and generates trees called cladograms. Cladistics also identifies clades, which are groups of organisms that include an ancestor species and its descendants.
      ::克拉迪斯是产生植物基因树的最广泛使用的方法,它以进化的祖先为基础,产生称为单形图的树木。 克拉迪斯也识别了克拉迪斯,即包括祖先物种及其后代在内的生物群。
    • Classifying organisms on the basis of descent from a common ancestor is called phylogenetic classification. Phylogenetic classification may or may not agree with Linnaean taxonomy, which is based on similarities in physical traits regardless of ancestry.
      ::根据共同祖先的血统对生物进行分类,称为植物遗传分类,基因遗传分类可能同意也可能不同意林纳纳分类学,后者基于身体特征的相似性,而不论其祖先为何。
    • The most direct evidence for evolutionary relationships is similarity in base sequences of the nucleic acids DNA and RNA. The more similar the base sequences of two species, the more closely related the species are assumed to be.
      ::进化关系的最直接证据是核酸DNA和RNA基准序列的相似性。 两种物种基序列越相似,该物种的关联就会越密切。

    Review
    ::回顾

    1. Define cladistics.
      ::定义单词。
    2. What does phylogenetic classification involve?
      ::植物遗传分类涉及什么?
    3. Why are nucleic acid base sequences directly related to evolution?
      ::为什么核酸基序列与进化直接相关?
    4. In cladogram 6 (lower right) of  Figure  , explain how the five species are related to one another.
      ::图1的单形图6(右下方)解释了这五个物种之间是如何相互联系的。
    5. Identify an ancestral trait and a derived trait in mammals. Explain your answer.
      ::识别哺乳动物的祖先特征和衍生特征 请解释一下答案
    6. Explain why a cladogram represents only one hypothesis about how evolution occurred.
      ::解释为什么单方形只代表一个假设 说明进化是如何发生的。
    7. Compare the advantages of Linnaean and phylogenetic classification systems.
      ::比较林内人和植物遗传分类系统的优点。