June 2007
Written by Eugene Wong, John Wilson & Robin Floyd

Tags: technology, barcode, technique

An Introduction to DNA Barcoding
During the course of our day-to-day lives we sometimes take for granted the immense variety of life (or ‘biodiversity') that surrounds us. In one country, such as Canada, there may be as many as 100,000 different species of animals, and if you take a step back and consider the entire world, you'd be looking at almost 2 million known animal species! That's just the ‘known' species (those described and named by scientists).

Nobody knows how many living species there really are on the planet - it could be many times that. The truth is, there's a lot of stuff out there and even if you wanted to, and you tried really hard, there's no way to keep in your head what everything is. It takes years of experience to become an expert in the identification of even a small animal group, and there are not many of these experts in the world.

Why would you want to know the species identity of every animal you come across? There are many answers to this question, and it depends on your interests. Some people want to: know if a particular insect is dangerous to their crops, help protect endangered species, or catch the smuggling of illegal animal products around the world. Many other people just have a basic curiosity about what we share the planet with. Regardless of the answer, there are more and more people asking today, “What is that?”

Currently, Canada is leading the way in one of the biggest biodiversity projects in the world - DNA barcoding. Traditionally, you tell one species from another by looking at its visual features: colours, shapes, and physical structures such as legs, fins or wings. But also, every living thing carries its own particular DNA, the set of genetic instructions controlling how it grows and develops. You've probably heard of genome sequencing – that is when you read the full set of DNA, or genome, belonging to a particular species such as a human or a fly.

The idea of DNA barcoding, proposed in 2003 by Dr. Paul Hebert from the University of Guelph, uses the same technology but takes a different approach – instead of reading every bit of DNA in one species, we read one small bit of DNA in lots of different species. That small piece can then be used to tell one species from another, similar to how a barcode uniquely identifies each product in a store. This means that whenever you come across an animal and you don't know what it is, you only need a small tissue sample –such as a feather, hair or insect leg – then you can read its DNA, scan its “barcode”, and you will know what that bug or bird is.

The gene chosen to act as the standardized "barcode" is called cytochrome oxidase I (COI). This gene plays an essential role in energy metabolism, so it is universally present in the genomes of all animals. It also appears to have just the right degree of variability in its exact sequence to tell apart most species. This makes it possible to apply the same technique to whatever comes along, whether studying crickets from the woods or a massive whale in the ocean. DNA barcoding results can be validated by examining more than one gene in crucial situations such as forensic entomology cases.

The first job is to collect specimens of known species, record their COI barcodes, and build up a database (such as the Barcode Of Life Data Systems or BOLD) which will match DNA sequences to species names to act like an ‘encyclopedia of life', for all to use.

The Barcode of Life Initiative is now a major international campaign with partners around the world, working together to barcode all animal life on the planet. It is a daunting challenge, but as technology continues to improve, DNA barcoding becomes faster and easier.

Now, just a few years after Dr. Hebert first introduced the DNA barcoding concept, the Canadian Centre for DNA Barcoding processes up to 100 000 specimens per year. Though samples still need to be sent to a molecular biology lab to get the barcode sequence for your unknown animal, technology is improving all the time and it is hoped that within a few years a portable device capable of scanning DNA will be invented. This would truly bring species identification out of the lab and available for everyone. DNA barcoding will help the world find many more answers to the question, “What is that?”

Also see Maggot: CSI to learn about the application of barcoding DNA technology in forensics.