What is DNA?

DNA is often referred to as the “building block of life”. This is because it stores, in coded form, all the genetic information needed to create a living being.

Discovering the structure of this amazing molecule was one of the most important scientific breakthroughs of the 20th century. The first description of DNA structure was published in 1953 by James Watson and Francis Crick. Their research would earn them the 1962 Nobel Prize in Medicine and Physiology.

The Process

Within their testing labs the DNA sequence services extract the DNA from your swab. This involves breaking the cells to release tiny quantities of DNA. Once this is separated from the rest of the cell it’s washed to ensure there are no contaminants. The DNA is then kept in tubes at a temperature of -20°C.

Your genome, your complete set of genes, is extremely large. There are 3 billion bases, or chemical components, grouped into 46 chromosomes. The specialists could analyze directly from this raw DNA but, to make the process much more efficient, they concentrate on a small region of around just 200-400 bases. The Procedure continues by obtaining the DNA sequence by employing a technique known as ‘polymerase chain reaction’, or PCR for short. PCR is at the core of much molecular biological work and its inventor, Dr. Cary Mullis, received the Nobel Prize in recognition of this. PCR allows a scientist to ‘zoom in’ on a short, specific stretch of DNA and then make copies of this region.

DNA Sequence services takes a small quantity of your DNA and adds it to a tube with some chemicals that will create a PCR reaction. These include some small pieces of DNA called primers, and some copies of the sequences as well as some other key nucleotides and enzymes. This mix is loaded onto a machine where it is alternately heated and cooled 20-40 times. This helps trigger the reaction and allows multiple copies of the relevant sequence to be completed. By the time the process has been completed, the tube will contain millions of copies of the stretch of DNA we are interested in.

The next step in the process is to determine the sequence of this amplified region. DNA sequence services does this using a technique known as automated fluorescent DNA sequencing, which, they admit is a bit of a mouthful.

They then carefully analyses your DNA sequence using computer software to identify the exact base positions that hold the key to your Y chromosome’s demographic history. By deducing what sites you are either ‘derived’ or ‘ancestral’ for, they can identify how you fit into the phylogenetic tree of worldwide Homo sapiens Y chromosomes. Or, in short, where your ancestors came from!

DNA - short for DeoxyriboNucleic Acid - is found within the nucleus of most types of cells. It contains the instructions for a cell and determines how a person's characteristics are passed from one generation to the next. Within the nucleus of a human cell, there are 23 pairs of chromosomes, making 46 chromosomes in total. Each chromosome consists of coiled chromatin which is composed of DNA wrapped around proteins called histones.

The 23 pairs of chromosomes within the nucleus are like the "instruction manual" for the development of a person. Whether a person has blue eyes or brown, or whether he or she has dark or blonde hair, is determined by DNA.

How can molecules (and strands of DNA are molecules) give "instructions"? To understand how this is possible, we should consider how we communicate and understand the textbooks, web sites and life's other "instruction manuals" from which we can get information.

At the most basic level we can only understand life's "instruction manuals" if they use acode that we can

understand. In the case of this web site, the code is called English or French. Your understanding of the text you are presently reading depends upon your understanding of the individual English or French words on this page. Furthermore, words seldom convey complete or understandable information. Information is better communicated by grouping words together, and as you already know, a set of words that conveys a complete thought is a sentence. The DNA language, just like English and French, consists of words and sentences too! Each "word" is a single unit of the DNA molecule called a nucleotide. Each "sentence" is a large string of nucleotides called a gene. Let's talk about the DNA words first.

Building Up a DNA Molecule: Nucleotides

DNA "words" are small molecules called nucleotides. The human genome, made up of 23 pairs of chromosomes, consists of a total of about 3 billion nucleotides. Each nucleotide consists of a backbone and a nitrogen-containing base. The backbone serves to attach one nucleotide to another.

All nucleotides have the same backbone (which is made up of a phosphate molecule and a special sugar molecule called deoxyribose). However, a nucleotide may have any one of four possible bases: Adenine (A), Cytosine (C), Guanine (G) or Thymine (T). Because there are only 4 different types of nucleotides that can make up DNA, there are only 4 "words" in the DNA language.

There is one other important aspect of nucleotides that we should discuss: Adenine (A) binds only to Thymine (T) and Cytosine (C) binds only to Guanine (G). Because of this, we say that A is complementary to T and that C is complementary to G. It is a lot easier to break up A-T and C-G bonds (which are called hydrogen bonds) than to break up the bonds that connect the nucleotide backbones together in the DNA chain (called covalent bonds). This property will become important later, when we discuss protein synthesis.

Building Up a DNA Molecule: How Nucleotides are Attached Together

DNA molecules actually consist of two parallel chains of nucleotides. Each chain is said to be complementary to the other, because each nucleotide on one chain binds to its complementary partner on the other. It might be useful to imagine the DNA molecule as a ladder, where the two long supporting pieces are composed of the nucleotide backbones fastened together, and the rungs are the complementary A-T and G-C base pairs. So if one side of the ladder had the sequence: AATGC, the complementary side would be TTACG.

In reality, the DNA ladder is twisted up into what is called a double helix conformation. Because the hydrogen bonds (connecting the G to the C, or the T to the A) are weaker than the covalent bonds connecting the individual nucleotides together, the two complementary chains which make up the twisted ladder can be easily unravelled and separated.