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How do scientists learn an individual’s DNA? – James, aged 11, Thame, UK
DNA (which stands for deoxyribonucleic acid) incorporates all the knowledge wanted to make your physique work. It’s also surprisingly easy.
DNA is comprised of 4 chemical constructing blocks, that are organized one after one another. This sequence is the instruction guide on your physique. The constructing blocks are referred to as adenine, thymine, guanine and cytosine, however we normally simply name them A, T, G and C.
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The knowledge in your DNA is bunched into sections referred to as genes. The genes are like sentences in an instruction guide.
Most genes management the on a regular basis operating of your physique – the way it grows hair, digests meals or carries oxygen round. So 99.9% of your DNA is strictly the identical as everybody else on the planet. The remaining is what makes you distinctive. For instance, when you’ve got blue eyes, then a number of of the letters in some genes shall be totally different from somebody with brown eyes.
As we develop, cells in our physique divide. One cell turns into two. Each time this occurs every of the brand new cells wants a full copy of DNA. DNA makes this straightforward, as a result of it’s fabricated from two strands. When a cell divides the strands break up up, and a brand new copy is made of every one. Let’s have a look at how that is completed.
The letter A on one strand is all the time reverse the letter T on the opposite, and G is all the time reverse C. So a brief double strand of DNA may seems like this:
Illustration of a double strand of DNA.
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Let’s see what occurs with one of many strands in a dividing cell. First a T is added reverse the primary A to make:
T pairs with A.
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Then an A will get hooked up to the T like this:
A pairs with T.
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Subsequent, C get positioned reverse G:
C pairs with G.
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And so forth till an entire new double-stranded piece of DNA is made.
Studying DNA
We are able to use this data of how DNA copies itself to learn an individual’s DNA.
To do that, a scientist places the DNA into 4 tubes. Then they add all of the equipment that the cell makes use of to repeat DNA, and many further As, Ts, Cs and Gs into every of the tubes.
Subsequent, they add some DNA letters which were modified to allow them to’t be a part of with the following letter within the sequence. You may consider them like items of Lego, however with flat tops so you’ll be able to’t add a brick on high of it. Let’s name these particular DNA letters A*, T*, G* and C*.
Every of our 4 tubes will get a few of the particular DNA letters added to it: A*s within the first tube, T*s within the second, G*s within the third and C*s within the fourth.
Let’s think about what occurs with our DNA sequence within the tube containing A*.
First, similar to earlier than, T is added reverse the primary A to make:
T pairs to A.
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Subsequent, although, an A* may get added to make this:
An A* is added.
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If this occurs, then the following letter can’t get hooked up to the A*. That is so long as this stretch of DNA will get.
However there’s lots extra DNA and letters within the tube and in some instances a standard A may have been added at that time, adopted by two Cs to make this:
Two Cs are added.
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Subsequent there’s a alternative once more. If an A* will get added the DNA sequence will seem like this:
Then an A*.
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Each time we attain the purpose the place we have to add an A there’s a probability an A* may get added, which stops the DNA getting any longer. So ultimately these DNA strands get made:
Completely different lengths of DNA.
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The scientist studying the DNA is aware of that every strand on this tube ends in an A*. She then counts what number of pairs are in every strand of DNA. By doing this, she will be able to work out that the 2nd, fifth and seventh letters are all As.
She then does precisely the identical factor with the opposite tubes and works out that the first and sixth letters are Ts, the third, 4th and ninth letters are Cs and the seventh is a G. By placing that every one collectively, she will be able to learn the entire DNA sequence.
Studying DNA is beneficial as a result of typically the letters within the genes aren’t fairly proper, like a misspelled phrase in a set of directions. This may trigger a few of your cells to not work correctly.
For instance, only one improper letter in a single explicit gene may imply somebody is extra more likely to change into diabetic, or get most cancers when they’re older. Studying somebody’s DNA permits medical doctors to identify and deal with these illnesses earlier than they change into too dangerous.
Mark Lorch doesn’t work for, seek the advice of, personal shares in or obtain funding from any firm or group that may profit from this text, and has disclosed no related affiliations past their educational appointment.
