Where do genes come from? - Carl Zimmer

基因是從哪來的？– 卡爾‧季默

譯者: Ya Hui Hung 審譯者: Regina Chu

You have about 20,000 genes in your DNA.

你的 DNA (脫氧核糖核酸) 含有大約 2 萬個基因

They encode the molecules that make up your body,

它們是結構成你身體的分子編碼

from the keratin in your toenails, to the collagen at the tip of your nose,

由腳指甲的角蛋白

鼻尖上的膠原蛋白

to the dopamine surging around inside your brain.

至在腦中浪湧的多巴胺

Other species have genes of their own.

其它物種也有自己的基因

A spider has genes for spider silk.

蜘蛛有製造蜘蛛絲的基因

An oak tree has genes for chlorophyll, which turns sunlight into wood.

橡樹有基因製造 將陽光轉換為木的葉綠素

So where did all those genes come from?

那這些基因是從哪來的呢?

It depends on the gene.

這取決於各基因

Scientists suspect that life started on Earth about 4 billion years ago.

科學家猜想，地球上的生命 起於大約 40 億年前

The early life forms were primitive microbes

早期的生命體是原始微生物

with a basic set of genes for the basic tasks required to stay alive.

有一組能應付維持 基本生命的基本基因

They passed down those basic genes to their offspring

它們將這些基本基因傳於

through billions of generations.

數十億的後代

Some of them still do the same jobs in our cells today, like copying DNA.

有些基因功能至今在我們的細胞中 仍然相同。例如，複製 DNA

But none of those microbes had genes for spider silk or dopamine.

但沒有一個微生物有可製造 蜘蛛絲或多巴胺的基因

There are a lot more genes on Earth today than there were back then.

比當時，現今地球上有多很多的基因

It turns out that a lot of those extra genes were born from mistakes.

原來，有很多額外的基因 是因為錯誤而誕生

Each time a cell divides, it makes new copies of its DNA.

每次細胞分裂， 就會製造新的 DNA 副本

Sometimes it accidentally copies the same stretch of DNA twice.

有時會意外地將同一段 DNA 複製兩次

In the process, it may make an extra copy of one of its genes.

在這過程中， 可能額外的複製了其基因之一

At first, the extra gene works the same as the original one.

起初，額外的基因功能和原基因無異

But over the generations, it may pick up new mutations.

但幾代後，可能會有新基因突變

Those mutations may change how the new gene works,

這些突變可能會改變這新基因的功能

and that new gene may duplicate again.

以及這新基因可能會再複製

A surprising number of our mutated genes emerged more recently;

數量驚人的基因突變出現於近期

many in just the past few million years.

很多在這過去的幾百萬年中發生

The youngest evolved after our own species broke off from our cousins, the apes.

最新的演變是在我們 與近親猿猴分開進化後

While it may take over a million years for a single gene to give rise

雖然由一個基因演變成一個基因家族

to a whole family of genes,

需要百萬年以上

scientists are finding that once the new genes evolve,

但科學家發現，只要新基因進化

they can quickly take on essential functions.

能很快地擔當基本功能

For example, we have hundreds of genes for the proteins in our noses

例如，鼻子裡有幾百個 捕捉氣味份子的

that grab odor molecules.

蛋白質基因

The mutations let them grab different molecules,

基因突變使得它們 能捕捉不同的分子

giving us the power to perceive trillions of different smells.

讓我們能感受到萬億不同的氣味

Sometimes mutations have a bigger effect on new copies of genes.

有時，突變對新的基因副本 有更大的影響

They may cause a gene to make its protein in a different organ,

有可能使一個基因所編碼的蛋白質 在不同的器官中表現

or at a different time of life,

或在不同的生命時間點表現

or the protein may start doing a different job altogether.

或有可能這蛋白質 有完全不同的功能

In snakes, for example, there's a gene that makes a protein for killing bacteria.

例如，蛇有一個基因 是製造可殺滅細菌的蛋白質

Long ago, the gene duplicated and the new copy mutated.

很久以前，這基因副本 在複製過程有了新突變

That mutation changed the signal in the gene

基因的信號因突變

about where it should make its protein.

而更改了其製造蛋白質的地點

Instead of becoming active in the snake's pacreas,

使原本在胰腺運作的蛋白質

it started making this bacteria-killing protein in the snake's mouth.

轉為在蛇口中殺滅細菌的蛋白質

So when the snake bit its prey, this enzyme got into the animal's wound.

所以當蛇咬著獵物時， 這酶侵入其傷口

And when this protein proved to have a harmful effect,

在證明這蛋白質是有害後

and helped the snake catch more prey,

能幫助蛇捕捉更多的獵物

it became favored.

它成為一項優勢

So now what was a gene in the pancreas makes a venom in the mouth

所以一個曾是在胰腺表現的基因 現今是蛇殺毀獵物

that kills the snake's prey.

在口中製造的毒液

And there are even more incredible ways to make a new gene.

不止如此，還有更令人難以置信的 新基因製造方式

The DNA of animals and plants and other species

動物、植物，及其它種類的 DNA

contain huge stretches without any protein coding genes.

含有大量沒有蛋白質編碼的基因片段

As far as scientists can tell, its mostly random sequences

據科學家所知 這些大都是隨機序列

of genetic gibberish that serve no function.

並無任何功能的基因亂碼

These stretches of DNA sometimes mutate, just like genes do.

如同基因 這些 DNA 片段有時也會突變

Sometimes those mutations turn the DNA into a place

有時，突變將 DNA

where a cell can start reading it.

轉換成為細胞能讀取的編碼

Suddenly the cell is making a new protein.

突然地，新蛋白質在細胞中誕生了

At first, the protein may be useless, or even harmful,

起先，這蛋白質可能是沒用的 或甚至是有害的

but more mutations can change the shape of the protein.

但更多的突變能轉換蛋白質的結構

The protein may start doing something useful,

而使蛋白質成為有用的

something that makes an organism healthier, stronger,

能讓生物體更健康、更強大

better able to reproduce.

增加其繁殖能力

Scientists have found these new genes at work in many parts of animal bodies.

科學家在動物體內多處 發現了新基因

So our 20,000 genes have many origins,

所以我們的 2 萬個基因有很多出處

from the origin of life, to new genes still coming into existence from scratch.

從生命的起源 至持續從零問世的基因

As long as life is here on Earth, it will be making new genes.

只要地球上有生命 就會有新基因誕生