mtDNA

Mitochondrial DNA is the small circular chromosome found inside mitochondria. These organelles found in cells have often been called the powerhouse of the cell.[1] The mitochondria, and thus mitochondrial DNA, are passed only from mother to offspring through the egg cell.

Mitochondrial DNA is the small circular chromosome found inside mitochondria. These organelles found in cells have often been called the powerhouse of the cell.[1] The mitochondria, and thus mitochondrial DNA, are passed only from mother to offspring through the egg cell.

Human mitochondrial DNA with the 37 genes on their respective H- and L-strands.

Mitochondrial DNA (mtDNA or mDNA)[3] is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, adenosine triphosphate (ATP). Mitochondrial DNA is only a small portion of the DNA in a eukaryotic cell; most of the DNA can be found in the cell nucleus and, in plants and algae, also in plastids such as chloroplasts.

In humans, the 16,569 base pairs of mitochondrial DNA encode for only 37 genes.[4] Human mitochondrial DNA was the first significant part of the human genome to be sequenced. In most species, including humans, mtDNA is inherited solely from the mother.

Since animal mtDNA evolves faster than nuclear genetic markers, it represents a mainstay of phylogenetics and evolutionary biology. It also permits an examination of the relatedness of populations, and so has become important in anthropology and biogeography.

Origin

Nuclear and mitochondrial DNA are thought to be of separate evolutionary origin, with the mtDNA being derived from the circular genomes of the bacteria that were engulfed by the early ancestors of today's eukaryotic cells. This theory is called the endosymbiotic theory.

线粒体DNA是在线粒体内发现的小的圆形染色体。在细胞中发现的这些细胞器通常被称为细胞的动力源。线粒体，也就是线粒体DNA，只能通过卵细胞从母亲传给后代。

人类线粒体DNA与各自的H和l链上的37个基因。

线粒体DNA (mtDNA或mDNA)[3]是位于线粒体中的DNA，是真核细胞内的细胞细胞器，将食物中的化学能转化为细胞可用的形式，即三磷酸腺苷(ATP)。线粒体DNA只是真核细胞DNA的一小部分;大多数DNA可以在细胞核中找到，在植物和藻类中也可以在叶绿体等质体中找到。

在人类中，16569对线粒体DNA碱基对只编码37个基因。人类线粒体DNA是人类基因组中第一个被测序的重要部分。在包括人类在内的大多数物种中，mtDNA仅从母亲那里遗传而来。

由于动物mtDNA的进化速度快于核遗传标记，因此它是系统发育和进化生物学的支柱。它还允许对人口的亲缘关系进行检查，因此在人类学和生物地理学中变得重要。

起源

细胞核和线粒体DNA被认为是独立的进化起源，mtDNA来自于被今天真核细胞的早期祖先所吞噬的细菌的环状基因组。这个理论被称为内共生理论。

Female inheritance

In sexual reproduction, mitochondria are normally inherited exclusively from the mother; the mitochondria in mammalian sperm are usually destroyed by the egg cell after fertilization. Also, most mitochondria are present at the base of the sperm's tail, which is used for propelling the sperm cells; sometimes the tail is lost during fertilization. In 1999 it was reported that paternal sperm mitochondria (containing mtDNA) are marked with ubiquitin to select them for later destruction inside the embryo. Some in vitro fertilization techniques, particularly injecting a sperm into an oocyte, may interfere with this.

The fact that mitochondrial DNA is maternally inherited enables genealogical researchers to trace maternal lineage far back in time. (Y-chromosomal DNA, paternally inherited, is used in an analogous way to determine the patrilineal history.) This is usually accomplished on human mitochondrial DNA by sequencing the hypervariable control regions (HVR1 or HVR2), and sometimes the complete molecule of the mitochondrial DNA, as a genealogical DNA test.[19] HVR1, for example, consists of about 440 base pairs. These 440 base pairs are then compared to the control regions of other individuals (either specific people or subjects in a database) to determine maternal lineage. Most often, the comparison is made to the revised Cambridge Reference Sequence. Vilà et al. have published studies tracing the matrilineal descent of domestic dogs to wolves.[20] The concept of the Mitochondrial Eve is based on the same type of analysis, attempting to discover the origin of humanity by tracking the lineage back in time.

mtDNA is highly conserved, and its relatively slow mutation rates (compared to other DNA regions such as microsatellites) make it useful for studying the evolutionary relationships—phylogeny—of organisms. Biologists can determine and then compare mtDNA sequences among different species and use the comparisons to build an evolutionary tree for the species examined. However, due to the slow mutation rates it experiences, it is often hard to distinguish between closely related species to any large degree, so other methods of analysis must be used.

女性继承

在有性繁殖中，线粒体通常只从母体遗传;哺乳动物精子中的线粒体通常在受精后被卵细胞破坏。此外，大多数线粒体位于精子尾部的底部，用于推动精子细胞;有时在受精过程中尾巴会脱落。1999年，有报道称，父亲精子线粒体(含有mtDNA)被泛素标记，以选择这些线粒体，以便在胚胎内被破坏。一些体外受精技术，尤其是将精子注入卵母细胞，可能会干扰这一过程。

线粒体DNA是母系遗传的这一事实，使系谱研究人员能够追溯到很久以前的母系谱系。(y染色体DNA是父系遗传的，以类似的方式用于确定父系历史。)这通常是通过测序人类线粒体DNA的高可变控制区域(HVR1或HVR2)，有时是线粒体DNA的完整分子，作为一个系谱DNA测试。例如，[19]HVR1由大约440个碱基对组成。然后将这440对碱基对与其他个体(数据库中的特定人群或受试者)的对照区域进行比较，以确定母系血统。大多数情况下，比较的对象是修改后的剑桥参考序列。Vila等人发表了追踪家养狗到狼母系血统的研究。线粒体夏娃的概念是基于同样类型的分析，试图通过追溯人类的世系来发现人类的起源。

mtDNA是高度保守的，其相对较慢的突变率(与其他DNA区域如微卫星相比)使其对研究生物进化关系(系统进化)非常有用。生物学家可以确定并比较不同物种间的mtDNA序列，然后利用这些比较为被检查的物种建立一个进化树。然而，由于其突变率较慢，往往很难在很大程度上区分亲缘关系较近的物种，因此必须使用其他分析方法。