two cells, one from each parent, found each other and became one.

分別來自父親和母親的兩個細胞，相遇並合而為一。

And that one cell reproduced itself, dividing, dividing, dividing, until there were 10 trillion of them.

接著這個細胞複製自己，分裂、 分裂、 再分裂，直到達到十兆個細胞。

Do you realize there are more cells in one person's body than there are stars in the Milky Way?

你知道人身體細胞的數目比銀河裡的星星還多嗎？

But those 10 trillion cells aren't just sitting there in a big pile.

但這十兆個細胞不只是隨便堆成一堆。

That would make for a pretty boring human being!

這樣的人類應該看起來很無趣吧！

So what is it that says a nose is a nose, and toes is toes?

那是什麼決定鼻子要成為鼻子、腳趾成為腳趾呢？

What is it that says this is bone, and this is brain, and this is heart, and this is that little thing in the back of your throat that you can never remember the name of?

什麼決定這個成為骨頭、那個成為大腦、那個成為心臟，和那個在你喉嚨深處的東西 ——那個你一直記不起名稱的東西？

Everything that you are or ever will be made of starts as a tiny link of instructions found in each and every cell.

任何組成你的部份都來自一份小小的、可在任何細胞中找到的說明書。

Every time your body wants to make something, it goes back to the instruction book, looks it up, and puts it together.

每次你的身體想要建造什麼東西時，都會回去看這本說明書，再進行建造。

So how does one cell hold all that information?

那細胞是如何保存這些資訊呢？

Let's get small.

我們縮小來看。

I mean, really small, smaller than the tip of a sewing needle.

我是說非常小，比針尖還小。

Then we can take a journey inside a single cell to find out what makes up the book of you, your genome.

然後我們走進細胞去探究這本書的組成：你的基因體。

The first thing we see is that the whole genome, all your DNA, is contained inside its own tiny compartment called the nucleus.

首先我們要瞭解基因體，也就是你所有的 DNA 被存放在一個叫做細胞核的小地方。

If we stretched out all the DNA in this one cell into a single thread, it would be over three feet long!

如果我們把一個細胞的 DNA 拉直成一條線，這條線會超過三英尺（約 91 公分）！

We have to make it fit in a tiny compartment that is a million times smaller.

我們必須把它裝進一個僅百萬分之一倍的小空間裡。

We could just bunch it up like Christmas lights, but that can get messy.

我們可以把它亂捲一通，像聖誔燈一樣，但這樣就太凌亂了。

We need some organization.

我們需要一些整理方法。

First, the long thread of DNA wraps around proteins clustered into little beads called nucleosomes, which end up looking like a long, beaded necklace.

首先，線狀的 DNA 會纏繞蛋白質，變成稱為核小體的小珠子， 它會看起來像是一條長長的串珠項鏈。

And that necklace is wrapped up in its own spiral like an old telephone cord.

接著，這條項鏈會繞成像是電話線一樣的螺旋。

And those spirals get layered on top of one another until we get a neat little shape that fits inside the nucleus.

再來，這些螺旋會相互交疊直到可以整齊地放進細胞核中。

Waaah! Three feet of DNA squeezed into a tiny compartment.

哇！三英尺的 DNA 就這樣擠進小小的空間。

If only we could hire DNA to pack our suitcases!

真希望我們可以用相同的機制打包行李！

Each tiny mass of DNA is called a chromosome.

每一小團 DNA 被稱為染色體。

The book of you would have 46 chapters, one for each chromosome.

在這本說明書中有 46 章，每一章就是一條染色體。

23 chapters of your book came from your mom, and 23 chapters came from your dad.

說明書的其中 23 章來自你的母親，另外一半則來自你的父親。

Two of those chapters, called "X" and "Y", determine if you are male, "XY", or female, "XX".

其中被稱為 X 和 Y 的兩章會決定你是男生，也就是 XY； 或是女生，也就是 XX。

Put them together and we get two almost identical but slightly different sets of 23 chapters.

它們會組成兩套幾乎相同卻又有些微差異的 23 個章節。

The tiny variations are what makes each person different.

這些微差異就造成了人與人之間的不同。

It's estimated that all the chapters together hold about 20,000 individual instructions, called genes.

如果把所有的章節都列入計算大約會有兩萬筆說明，也就是基因。

Written out, all those 20,000 instructions are 30 million letters long!

如果把這兩萬筆說明全部寫下來會長達三千萬個字母！

If someone were writing one letter per second, it would take them almost an entire year to write it once.

如果人可以一秒鐘寫一個字母，那也需要花將近一年才能寫完一次。

It turns out that our genome book is much, much longer than just those 30 million letters, almost 100 times longer!

然而，我們的說明書比三千萬個字母還長將近一百倍！

What are all those extra pages for?

那這些多餘的書頁又寫了些什麼呢？

Well, each set of instructions has a few pages of nonsense inserted that have to be taken out before we end up with something useful.

每部份的說明都會插入幾頁無意義的編碼。我們必須先將這些亂碼移除才能看到有意義的資訊。

The parts we throw out, we call introns.

這部份我們移除的亂碼被稱為內插子。

The instructions we keep, we call exons.

而保留下來的資訊被稱為外顯子。

We can also have hundreds of pages in between each gene.

我們的基因與基因之間也可能有幾百頁的亂碼。

Some of these excess pages were inserted by nasty little infections in our ancestors, but some of them are actually helpful.

有些是在我們的祖先被病毒感染時所插入的多餘頁面。 但也有些看似無意的頁面是有用的。

They protect the ends of each chapter from being damaged, or some help our cells find a particular thing they are looking for, or give a cell a signal to stop making something.

它們可以保護章節的頭尾免於破壞，或當作索引， 也有可能是當作停止製造的訊號。

All in all, for every page of instructions, there's almost 100 pages of filler.

總而言之，在每部份說明中大約包含了一百頁的內容。

In the end, each of our books' 46 chapters is between 48 and 250 million letters long.

最後，我們書的 46 章會介於四千八百萬到二億五千萬個字母長。

That's 3.2 billion letters total!

共計三十二億個字母！

To type all that copy, you would be at it for over 100 years, and the book would be over 600,000 pages long.

若以打字方式複製，你需要花上一百年，而且這本書會超過六十萬頁。

Every type of cell carries the same book, but each has a set of bookmarks that tell exactly which pages needs to look up.

每一種細胞都帶有相同的說明書，但是會有不同的索引幫助搜尋需要看的頁面。

So a bone cell reads only the set of instructions it needs to become bone.

所以骨細胞只會看和生成骨頭相關的指引。

Your brain cells, they read the set that tells them how to become brain.

你的腦細胞會閱讀組成大腦所需的部份。

If some cells suddenly decide to start reading other instructions, they can actually change from one type to another.

如果一個細胞突然開始閱讀其他的指引，它們就會從一種細胞轉換成另一種。

So every little cell in your body is holding on to an amazing book, full of the instructions for life.

你身體裡每一個細胞都帶著這本神奇的書，這本書充滿對生命所有的註解。

Your nose reads nose pages, your toes read toes pages, and that little thing in the back of your throat, it's got its own pages too.

你的鼻子閱讀關於鼻子的部份，你的腳趾則閱讀關於腳趾的部份， 而你喉嚨深處的那個小東西也有屬於自己的章節。

They are under uvula.

就是標示「懸雍垂」的那幾頁。