The genes you don't get from your parents (but can't live without) - Devin Shuman

翻译人员: Wang Pray 校对人员: Yanyan Hong

Inside our cells, each of us has a second set of genes

在我们的细胞内， 我们每个人都有第二套基因

completely separate from the 23 pairs of chromosomes

与我们从父母那里继承的

we inherit from our parents.

23 对染色体完全分开。

And this isn’t just the case for humans—

而且这不仅仅是人类的情况——

it’s true of every animal, plant, and fungus,

每种动物、植物和真菌，

and nearly every multicellular organism on Earth.

以及几乎所有地球上 每个多细胞的生物体都是如此。

This second genome belongs to our mitochondria,

这第二个基因组属于我们的线粒体，

an organelle inside our cells.

是我们细胞内的一个细胞器。

They’re not fully a part of us, but they’re not separate either—

他们并不完全是我们的一部分， 但它们也不是独立的——

so why are they so different from anything else in our bodies?

那么，为什么它们与我们身体里的 其他东西如此不同？

Approximately 1.5 billion years ago,

大约 15 亿年前，

scientists think a single-celled organism engulfed the mitochondria’s ancestor,

科学家认为一个单细胞生物体 吞噬了线粒体的祖先，

creating the predecessor of all multicellular organisms.

进而创造了所有多细胞生物的前身。

Mitochondria play an essential role:

线粒体起着至关重要的作用：

they convert energy from the food we eat and oxygen we breathe

它们从我们吃的食物 和呼吸的氧气中的能量

into a form of energy our cells can use, which is a molecule called ATP.

转化为我们细胞可以使用的能量形式， 这就是一种叫做 ATP 的分子。

Without this energy, our cells start to die.

没有这种能量， 我们的细胞就会开始死亡。

Humans have over 200 types of cells,

人类有超过 200 种类型的细胞，

and all except mature red blood cells have mitochondria.

而除了成熟的红细胞外， 都有线粒体。

That’s because a red blood cell’s job is to transport oxygen,

这是因为红细胞的工作是运输氧气，

which mitochondria would use up before it could reach its destination.

而线粒体在它到达目的地之前就会耗尽。

So all mitochondria use oxygen and metabolites to create energy

因此，所有线粒体都使用氧气 和代谢物来产生能量，

and have their own DNA,

并有自己的 DNA 。

but mitochondrial DNA varies more across species than other DNA.

与其他 DNA 相比， 线粒体 DNA 在不同物种间的差异更大。

In mammals, mitochondria usually have 37 genes.

在哺乳动物中， 线粒体通常有 37 个基因。

In some plants, like cucumbers, mitochondria have up to 65 genes,

在一些植物中，如黄瓜， 线粒体有多达 65 个基因，

and some fungal mitochondria have only 1.

而一些真菌的线粒体只有 1 个。

A few microbes that live in oxygen-poor environments

一些生活在贫氧环境中的微生物

seem to be on the way to losing their mitochondria entirely,

似乎正在走向完全失去 他们的线粒体的路上，

and one group, oxymonad monocercomonoides, already has.

而类单鞭滴虫属的这些生物 已经开始没有线粒体了。

This variety exists because mitochondria are still evolving,

这种多样性的存在 是因为线粒体仍在进化中，

both in tandem with the organisms that contain them,

与含有它们的生物体，

and separately, on their own timeline.

分别在自己的时间线上同步进行。

To understand how that’s possible,

要了解这一点是如何实现的，

it helps to take a closer look at what the mitochondria inside us are doing,

仔细看看我们体内的 线粒体在做什么会有所帮助，

starting from the moment we’re conceived.

从我们受孕的那一刻开始。

In almost all species, mitochondrial DNA is passed down from only one parent.

在几乎所有物种中，线粒体 DNA 只从父母一方传下来。

In humans and most animals, that parent is the mother.

在人类和大多数动物中。 该受体是母亲。

Sperm contain approximately 50 to 75 mitochondria in the tail,

精子的尾部大约含有 50 至 75 个线粒体，

to help them swim.

来帮助他们游动。

These dissolve with the tail after conception.

这些东西在受孕后与尾巴一起解体。

Meanwhile, an egg contains thousands of mitochondria,

同时，一个卵 含有成千上万的线粒体，

each containing multiple copies of the mitochondrial DNA.

每个都含有多组线粒体 DNA 。

This translates to over 150,000 copies of mitochondrial DNA

这意味着我们体内 超过 15 万份的线粒体 DNA

that we inherit from our mothers,

是从母亲那里继承的。

each of which is independent and could vary slightly from the others.

每一个都是独立的， 且彼此之间可能略有不同。

As a fertilized egg grows and divides,

随着受精卵的生长和分裂，

those thousands of mitochondria are divvied up into the cells

这些数以千计的线粒体被分配到

of the developing embryo.

发育中的胚胎细胞中。

By the time we have differentiated tissues and organs,

当我们有了分化的组织和器官，

variations in the mitochondrial DNA are scattered at random throughout our bodies.

线粒体 DNA 的变异是 随机地散布在我们的身体里。

To make matters even more complex,

使之更复杂的是，

mitochondria have a separate replication process from our cells.

线粒体有一个 与我们细胞不同的独立复制。

So as our cells replicate by dividing, mitochondria end up in new cells,

因此，当我们的细胞通过分裂进行复制时， 线粒体最终出现在新细胞中，

and all the while they’re fusing and dividing themselves,

而它们在自己的时间轴上

on their own timeline.

融合和分裂。

As mitochondria combine and separate,

随着线粒体的结合和分离，

they sequester faulty DNA or mitochondria that aren’t working properly for removal.

它们封存了有问题的 DNA 或 对不正常工作的线粒体进行清除。

All this means that the random selection of your mother’s mitochondrial DNA

所有这一切意味着， 你在出生时从母亲那随机

you inherit at birth

继承的线粒体 DNA

can change throughout your life and throughout your body.

会在你的一生中 在你身上发生改变。

So mitochondria are dynamic and, to a degree, independent,

所以线粒体是动态的，而且， 在某种程度上是独立的，

but they’re also shaped by their environments: us.

但它们也被他们的环境所塑造：我们。

We think that long ago,

我们认为，很久以前，

some of their genes were transferred to their host’s genomes.

它们的一些基因被转移到 宿主的基因组中。

So today, although mitochondria have their own genome

所以今天，虽然线粒体 有自己的基因组，

and replicate separately from the cells that contain them,

并与包含它们的细胞分别进行复制，

they can't do this without instruction from our DNA.

如果没有我们的 DNA 指示， 它们就不能这样做。

And though mitochondrial DNA is inherited from one parent,

而尽管线粒体 DNA 是由父母一方遗传的，

the genes involved in building and regulating the mitochondria

参与建立和调节线粒体的基因

come from both.

来自父母双方。

Mitochondria continue to defy tidy classification.

线粒体继续藐视着井井有条的分类。

Their story is still unfolding inside of each of our cells,

它们的故事仍在 我们每个人的细胞里展开，

simultaneously separate and inseparable from our own.

同时独立且与我们自己不可分割。

Learning more about them can both give us tools

更多地了解它们，既可以给我们提供

to protect human health in the future, and teach us more about our history.

在未来保护人类健康的办法， 还能让我我们更多地了解我们的历史。