垃圾DNA(z)

ereree

Junk DNA
垃圾DNA

In molecular biology, \"junk\" DNA is a collective label for the portions of the DNA sequence of a chromosome or a genome for which no function has yet been identified. About 98.5% of the human genome has been designated as \"junk\", including most sequences within introns and most intergenic DNA.
在分子生物学里，“垃圾”DNA就是染色体或基因组部分排序的统称，它们的作用一直没有被确定。大约98.5%的人类基因被指定为“垃圾”，包括基因内区多数排序和大多数基因间的DNA。
While much of this sequence is probably an evolutionary artifact that serves no present-day purpose, some may function in ways that are not currently understood. In fact, recent studies have suggested functions for certain portions of what has been called junk DNA. Moreover, the conservation of some \"junk\" DNA over many millions of years of evolution may imply an essential function. The \"junk\" label is therefore recognized as something of a misnomer, and many prefer the more neutral term \"noncoding DNA\". codE
虽然多数排序或许是一个不适应现今需要的人造物品，有些可能以现今不理解的方式发生作用。事实上，近来的研究已经提出一部分所谓的垃圾DNA的功能。而且，某些保持了上千万年进化的“垃圾”DNA也意味着一个基本的功能。“垃圾”的分类因此被认为是有点用词不当，而多数人更喜欢中性的说法“非编码DNA”
Broadly, the science of functional genomics has developed widely accepted techniques to characterize protein-coding genes, RNA genes, and regulatory regions. In the genomes of most plants and animals, however, these together constitute only a small percentage of genomic DNA (less than 2% in the case of humans). The function of the remainder, if any, remains under investigation. Most of it can be identified as repetitive elements that have no known biological function (although they are useful to geneticists for analyzing lineage and phylogeny). Still, a large amount of sequence in these genomes falls under no existing classification other than \"junk\".
广泛地，遗传作用的科学得到广泛地发展，形成了表现蛋白质编码因子RNA因子和调整区域普遍公认的技术。然而在大多数动植物基因组内，这些加起来只占遗传DNA很小的百分比（在人类情形里小于2%）。剩下的作用，即使任何一种，仍处于研究中。它们多数被认为是没有熟知的生物学功能的重复元素(尽管它们对遗传学家分析血统和发展史是有用的)。然而，这些基因组的大量排序没有成为而非“垃圾”的现今分类。
Overall genome size, and by extension the amount of junk DNA, appears to have little relationship to organism complexity: the genome of the unicellular Amoeba dubia has been reported to contain more than 200 times the amount of DNA in humans. The pufferfish Takifugu rubripes genome is only about one tenth the size of the human genome, yet seems to have a comparable number of genes. Most of the difference appears to lie in what is now known only as junk DNA. This puzzle is known as the \"C-value enigma\" or, more conventionally, the \"C-value paradox\"[
整个基因组的大小以及根据垃圾DNA量的范围，好象与生物体的关系不大：据说变形虫的单细胞基因组含有200倍以上人类DNA数量。pufferfish Takifugu rubripes基因只是人类基因的大约十分之一，然而好象有了一个可比较的基因数量。大多数的差异好象在于不熟悉的如垃圾DNA那样。这个困惑就是熟知的“C-值迷”或者更为传统的“C-值悖论”。
Hypotheses of origin and function
起源和作用假定
There are many hypotheses, none conclusively established, for how junk DNA arose and why it persists in the genome:
有很多假使，最后没有一个被确定，如垃圾DNA怎样激活以及为什么存在于基因组中：
•  These chromosomal regions could be composed of the now-defunct remains of ancient genes, known as pseudogenes, which were once functional copies of genes but have since lost their protein-coding ability (and, presumably, their biological function). After non-functionalization, pseudogenes are free to acquire genetic noise in the form of random mutations.
•  这些染色体区域可能由现在死亡的远古基因残余组成，如熟悉的假基因，它们曾经发挥过基因复制功能只是已经丧失了蛋白质编码能力（大概为它们的生物学作用）。在非作用下，假基因以随机突变的方式自由地获得遗传噪音。
•  8% of the junk DNA has been shown to be formed by retrotransposons of Human Endogenous Retroviruses (HERVs), although as much as 25% is recognisably formed of retrotransposons.
•  8%的垃圾基因已经表明由人类内的逆转录酶病毒(HERVs)逆转录因子构成，尽管认可形成的只有25%多。
•  Junk DNA may act as a protective buffer against genetic damage and harmful mutations. For example, a high proportion of nonfunctional sequence makes it unlikely that a functional element will be destroyed in a chromosomal crossover event, possibly making a species more tolerant to this important mechanism of genetic recombination.
•  垃圾DNA也许在抗拒遗传破坏和有害突变方面扮演着保护缓冲的角色。例如，比例高的非功能排序就使得它在一次染色体搭桥事件中不太可能受到破坏，或许使得物种朝这个遗传再结合的重要机制方面更有耐受性。
•  Junk DNA might provide a reservoir of sequences from which potentially advantageous new genes can emerge. In this way, it may be an important genetic basis for evolution.
•  垃圾DNA或许提供了一个排序库，从这个库里潜在有利新基因能够显现。以这个方式，它也许是一个进化的重要遗传元素。
•  Some junk DNA could simply be spacer material that allows enzyme complexes to form around functional elements more easily. In this way, the junk DNA could serve an important function even though the actual sequence information it contains is irrelevant.
•  某些垃圾DNA或许只是允许酶更容易合成形成周围功能元素的中间材料。以这种方式，垃圾DNA就可以起一个重要作用甚至它拥有的实际排序信息是不相关的。
•  Some portions of junk DNA could serve presently unknown regulatory functions, controlling the expression of certain genes and/or the development of an organism from embryo to adult.Junk DNA may serve other, unknown purposes. For example, some non-coding RNAs have been discovered in what had been considered junk.
•  某些垃圾DNA目前可能起未知名的调整作用，控制某个基因表达和/或者控制有机体从胚胎到成熟期的演化。垃圾DNA或许起其它作用，未知名的意图。例如，某些非编码RNA已经以被一直认为的垃圾方式被发现。
•  Junk DNA may have no function. For example, recent experiments removed 1% of the mouse genome and were unable to detect any effect on the phenotype. This result suggests that the DNA is, in fact, non-functional. However, it remains a possibility that there is some function that the experiments performed on the mice were merely insufficient to detect.
垃圾DNA也许没有功能。例如，近来的实验排除了1%的老鼠基因而不能够来测定任何显性作用。事实上这个结果提到DNA是非功能的。然而，它仍拥有具备一些功能的可能性，在老鼠身上进行的实验只不过不足于来测定发现而已。
Evolutionary Conservation of \"junk\" DNA
“垃圾” DNA的进化保存
Comparative genomics is a promising direction in studying the function of junk DNA. Biologically functional sequences, as the theory goes, tend to undergo mutation at a slower rate than nonfunctional sequence, since mutations in these sequences are likely to be selected against. For example, the coding sequence of a human protein-coding gene is typically about 80% identical to its mouse ortholog, while their genomes as a whole are much more widely diverged. Analyzing the patterns of conservation between the genomes of different species can suggest which sequences are functional, or at least which functional sequences are shared by those species. Functional elements stand out in such analyses as having diverged less than the surrounding sequence.
基因比较在研究垃圾DNA方面是有希望的方法。生物功能排序，如理论进行的那样，往往是比非功能排序以较低速度经历突变，因为在这些排序里突变很可能是选择保护。人类蛋白质编码因子编码排序与其老鼠ortholog 相比典型地具有大约80%的同一性，虽然它们的基因组整体上有更多分*。分析不同物种间基因组保存模式就能使人想起排序是功能性的，或者至少它们的功能性排序被那些物种共同分享。以这种分析如具有的分*建立的功能元素小于周围的排序。
Comparative studies of several mammalian genomes suggest that approximately 5% of the human genome has evolved under purifying selection since the divergence of the mammals. Since known functional sequence comprises less than 2% of the human genome, it appears that there may be more functional \"junk\" DNA in the human genome than there is known functional sequence.
几个哺乳动物的基因组比较研究提出大约5%的人类基因组在自从哺乳动物分歧以来提纯选择下进化。由于已知的功能性排序由2%人类基因组组成，这好象在人类基因组内比已知的功能性排序可能有更多功能性“垃圾”DNA。
A surprising recent finding was the discovery of nearly 500 ultraconserved elements, which are shared at extraordinarily high fidelity among the available vertebrate genomes, in what had previously been designated as junk DNA. The function of these sequences is currently under intense scrutiny, and there are preliminary indications that some may play a regulatory role in vertebrate development from embryo to adult.
一项令人惊讶的新近发现就是将近500种极端保存元素的发现，它们在有用的脊椎动物基因组分享中保真度很高，这其中先前已认定为垃圾DNA。这些排序的功能目前处于严格的审查中。初步表明有些或许在脊椎动物从胚胎到成熟阶段的发展中扮演着调整角色。
It must be noted that all present results concerning evolutionarily conserved human \"junk\" DNA are expressed in highly preliminary, probabilistic terms, since only a handful of related genomes are available. As more vertebrate, and especially mammalian, genomes are sequenced, scientists will develop a clearer picture of this important class of sequence. However, it is always possible, though highly unlikely, that there are significant quantities of functional human DNA that are not shared among these species, and which would thus not be revealed by these studies.
必须指出的是目前所有涉及进化保存人类“垃圾”DNA的结果以高度预备的方式来表达，也就是，因为只有少数有关的基因能用得到。如更多脊椎动物，尤其是哺乳动物，基因组是排序了的，科学家将揭示这个重要的排序分类更清楚的图景。然而，这总是可能的，虽然很不确定，人类功能性DNA的重要数量没有在这些物种间分享，而因此*这些研究不能揭示出来。
On a theoretical note, it is often observed that the presence of high proportions of truly nonfunctional \"junk\" DNA would seem to defy evolutionary logic. Replication of such a large amount of useless information each time a cell divides would waste energy.
根据理论说明，可以观察到出现比例很高真正非功能性垃圾“DNA”就好象是违反进化逻辑的。一个细胞每次分裂这类大量信息的复制就会浪费能量。
Organisms with less nonfunctional DNA would thus enjoy a selective advantage, and over an evolutionary time scale, nonfunctional DNA would tend to be eliminated. If one assumes that most junk DNA is indeed nonfunctional, then there are several hypotheses for why it has not been eliminated by evolution:
具有很少非功能性DNA的生物体就享受着选择优势的乐趣，而经过一个进化周期，非功能性DNA就往往被消除了。如果大多数垃圾DNA假定为真正非功能性的，那么就有好几种假使，为什么*进化一直没有清除它：
•  The energy required to replicate even large amounts of nonfunctional DNA is in fact relatively insignificant on the cellular or organismal scale, so no selective pressure results (selection coefficients less than one over the population size are effectively neutral);
•  需要用来复制即使大量的非功能性DNA的能量事实上在细胞或生物体范围内相对地没有意义，因此没有选择的压力结果(超过人口大小的选择系数小于一是有效中性的)；
•  The aforementioned possible advantage of having extra DNA as a reservoir of potentially useful sequences; and
•  前述具备额外的DNA可能优势如同一个有用系列的潜在库；而
•  Retrotransposon insertions of nonfunctional sequence occurring faster than evolution can eliminate it. These are all hypotheses for which the time scales involved in evolution may make it difficult for humans to investigate rigorously.
•  逆转录因子 插入非功能性排序事件比进化能够清除它要快得多。这些是全部的假设，对于此假使涉及进化的时间比例或许使得人类严格研究它非比易事。
- Wikipedia
NEWS ARTICLES
新闻文章
Salvage prospect for 'junk' DNA BBC - April 26, 2006
‘垃圾DNA’的勘查BBC–2006年4月26
  
What Is Junk DNA, And What Is It Worth? Science Daily - February 2005
什么是垃圾DNA, 它们的作用又是什么? 每日科学–2005年2月
Scientists Uncover Clues To The Mystery Of 'Gene Deserts' Science Daily - December 2004
科学家揭示通向‘遗传荒漠’的神秘线索每日科学-2004年12月
Gene deserts are long stretches of DNA between genes that were once thought to have no biological function, and were dismissed as \"junk DNA.\" As scientists probe deeper into the DNA's double helix, however, they are discovering that many of these \"non-coding\" segments actually play an important role in regulating gene activity.
遗传荒漠是基因间很长的一段，曾被认为没有生物功能，而被做为“垃圾DNA”忽略。然而当科学家探测更深入进入DNA双螺旋内，他们发现许多这类“非编码”片段实际上在调节基因行为方面扮演一个重要角色。
'Junk' throws up precious secret DNA BBC - May 2004
‘垃圾'扔掉了宝贵隐秘的DNA BBC-2004年5月

Researchers inspecting the genetic code of rats, mice and humans were surprised to find they shared many identical chunks of apparently \"junk\" DNA.
研究人员检查了老鼠的基因代码，令人惊讶地发现老鼠与人类共享“垃圾”DNA明显的主干。
Research De-mystifies Origins Of 'Junk' DNA Science Daily - March 26, 2004
‘垃圾'DNA起源的判定困惑每日科学-2004年三月26日。
GENETICS
遗传学
PHYSICAL SCIENCES INDEX
物理科学索引
ALPHABETICAL INDEX OF ALL FILES
按字母顺序排列的所有文件索引
CRYSTALINKS MAIN PAGE
水晶连接网站主页
http://www.crystalinks.com/junkdna.html