A Simple Beginners Guide to DNA

So you’ve heard about DNA fingerprinting, DNA paternity tests and diseases caused by mutations in DNA. But what does any of that really mean to you? Let’s start with the basics and take an easy introduction to what DNA is and how yours is different from anyone else.

What is DNA?

Let’s think of DNA as a big instruction manual for building a person. It has lots of details about how tall you can be, what color to make your eyes, and even how much at risk you will be for certain diseases. Every cell in your body has a copy of this DNA instruction manual. The cell reads your DNA book to get the information it needs to build hair, fingernails, liver, brain, your heart and so on for every part of your body. Everyone has pretty much the same DNA instruction manual as you do. If you could read someone else’s DNA you’d find that it’s about 99.9% the same as yours. But we aren’t all the same height, or have the same eye color so these differences are in the tiny 0.1% of your DNA. It might sound like a small amount of variation between people, but this is what has let us develop DNA fingerprinting and DNA paternity testing.

What is DNA Made of?

Just like a book your DNA instruction manual is made up of letters. It’s pretty simple though, it has only 4 different letters; A, T, G, C. These letters are enough to spell out all the instructions needed to tell your cells to divide and grow and eventually develop into you. Since the instructions are written using only 4 letters, you might want to think of it being written in a type of secret code. So your DNA is in code and just like the cryptic coded messages you’ve seen in spy movies, your DNA needs to be translated in order for it to makes sense. Obviously the cells of your body can read the instructions from it just fine, and we can too - this is where DNA testing comes into play. Scientists have a technique called sequencing where they can read off each letter one at a time until we have the whole book, or at the very least, enough bits to make sense of. You might have heard a couple of years ago that the Human Genome Project finished decoding the entire sequence of human DNA. To do this though, they needed a massive team of international scientists working for almost 10 years to decode just one persons DNA instruction manual. The technology used to sequence DNA has improved massively recently, but unfortunately it’s still not practical to completely decode any single individual. This is mainly because your DNA instruction manual is huge, on the scale of billions and billions of letters.

How is my DNA arranged?

It might seem impossible that you could code enough information to build a human with only the 4 letters A, T, G and C, but your DNA manual is long. Really really long. These 4 letters are repeated billions of times in different combinations and arrangements. If we think of your DNA instruction manual as a book where every letter of every word is taken off the page and placed out into a straight line it would fill up your house in no time and make it impossible for you to find any specific bits of information you were looking for. Lucky for us DNA is arranged neatly - like a book. We can divide books into chapters and the equivalent also happens in your DNA instruction manual. The long strings of letters are arranged neatly into a defined order, and then the whole lot is divided up into chunks called chromosomes. Humans have 23 different chromosomes, with each one containing different bits of information on how to build our body. Each of these chromosomes is identified by a number (1, 2, 3 etc.) except for two; the X-chromosome and the Y-chromosome. And this brings us to the first major difference you’ll see between people - sex. If you have only copies of the X-chromosome then you are female, if you have the Y-chromosome then you are male. These two chapters of your DNA instruction manual contain all the information needed to tell your body how to develop as a male or a female.

So what about that 0.1% difference between people?

This is at the heart of how most DNA tests work. It’s the differences between our DNA instruction manuals (as small as one letter out of millions) that scientists can read in ancestry, fingerprinting and disease screening tests. Because every cell in your body has a copy of your DNA manual, the material for a test can come from just about anywhere; a hair root, cheek swab, blood test and so on.
We’re going to go into each of these types of tests and how they work in more depth, with each having their own simple beginners guide. Check out the Simple guide archive from the links to your left or from the homepage to find the type of test you’d like more information about.