DNA Testing

What is DNA?

Just what is DNA?

DNA or Deoxyribonucleic Acid, is the name given to a very complex molecule stored in the nucleus (hence the “nucleic” part of the name) of every cell in your body.  DNA is the biological blueprint of the body.  Every last minute detail of your body’s structure is encoded in your DNA—from your height, eye color, the sound of your voice, you name it, it’s in there somewhere.

As you’ve probably deduced, DNA is incredibly long and incredibly complex.  However, its basic structure is really quite simple—it’s set up like a ladder, with two long side pieces and “rungs” composed of units called nucleotides.  There are only (believe it or not) 4 types of nucleotides—Adenine, Thymine, Cytosine, and Guanine.  These are usually abbreviated as A, T, C, and G.

The exact sequence of these nucleotides determines all physical characteristics of an organism.  It constitutes an instruction manual for the cell’s system, so anything the cell does is determined by the order of nucleotides.  If you know anything about computers, this system should be familiar to you—it’s very similar to the storage of binary information on a hard drive.  Yes, that’s right, you’ve got a microscopic hard drive in every cell in your body that contains all the stuff that makes you you—pretty wild, isn’t it?
For example, a sequence like:
ATTCGAGGGTAAGC
may tell the body “bright blue eyes!” while the sequence:
ATTCGGAGTCAATT
would tell the body “dark brown eyes!”

Now, these 4 nucleotides come in pairs—A always pairs with T, and C always pairs with G.  Thus the two sides of the DNA “ladder” will always mirror each other. So, a textual representation of the “blue eyes” DNA sequence above would look something like this:

|-A—T-|
|-T—A-|
|-T—A-|
|-C—G-|
|-G—C-|
|-A—T-|
|-G—C-|
|-G—C-|
|-G—C-|

This double sided mirror structure is very important, because this is how the DNA molecule “communicates” with the rest of the cell.  The DNA makes a “photocopy” of itself called RNA or Ribonucleic acid (sometimes called mRNA or messenger RNA) and sends it out to the main body of the cell, which then instructs the protein assembly factories in the cell (called ribosomes) as to exactly which proteins they are to create. 

The process of photocopying is called DNA transcription.  The DNA molecule essentially splits down the middle, the cell assembles the appropriate mirror image for each half, after which the two halves of the original DNA molecule reunite.

In other words, if we begin with the above DNA sequence, and transcription begins, we’d see the following:

|-A-                       -T-|
|-T-                        -A-|
|-T-                        -A-|
|-C-                       -G-|
|-G-                       -C-|
|-A-                       -T-|
|-G-                       -C-|
|-G-                       -C-|
|-G-                       -C-|

Then the two sides are copied as follows:

|-A-  U-|                 |-A  -T-|
|-T-  A-|                 |-U  -A-|
|-T-  A-|                 |-U  -A-|
|-C-  G-|                 |-C  -G-|
|-G-  C-|                 |-G  -C-|
|-A-  U-|                 |-A   -T-|
|-G-  C-|                 |-G  -C-|
|-G-  C-|                 |-G  -C-|
|-G-  C-|                 |-G  -C-|

You may have noticed that in the RNA strands the letter U has taken the place of the letter T.  That’s not a mistake—in RNA there is no thymine, it’s replaced by a nucleotide called uracil.  The RNA then is sent to the ribosome, and the “blue eyes” proteins are produced.

Every single cell in your body contains DNA, which means that one can tell just about everything about your body structure from analyzing just one cell.  That’s why many DNA tests only require a cheek sample (cheek samples are used because it is very easy to obtain whole undamaged cells from the inside of your cheek).

Each cell in your body contains organelles, or tiny cell organs, each with it’s own special function.  The central organelle in every cell is called the nucleus, and in the center of the nucleus lies the nucleolus.  Inside the nucleolus sits your DNA.

Inside the nucleolus, DNA is organized into chromosomes.  Each chromosome has it’s own unique shape and function. A human being has 23 chromosomes, each one containing thousands of DNA segments.

Both a sperm and an egg cell contain exactly half of the parents' DNA, and when they unite a new, full set of DNA is formed. Therefore, every child has half of his or her father's DNA and half of the mother's. This is what makes DNA paternity tests as well as DNA maternity tests possible.

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