DNA, or deoxyribonucleic acid, is the hereditary material found in most organisms (including dogs). Nearly every cell in a dog’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA).
The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.
DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a 'double helix'. The structure of the double helix is like a ladder, with the base pairs forming the ladder’s rungs & the sugar and phosphate molecules forming the vertical 'steps' of the ladder.
DNA Chain
An important property of DNA is that it can replicate, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell.
DNA Testing
When DNA is collected via blood or cheek skin cells, the DNA is processed using PCR (Polymerase chain reaction) which allows isolation of DNA fragments from genomic DNA by selective amplification of a specific region of DNA.
The suspect DNA molecules are put into a small plastic tube with synthetic molecules of single stranded DNA (usually 20-30 nucleotides) called 'primers'. Primers are designed to match with specific sequences in the DNA strand & two different primers are used to bracket the target region to be amplified.
One primer is complementary to a DNA strand at the beginning of the target region; a second primer is complementary to a sequence on the opposite DNA strand at the end of the target region. It is worth noting that the target region need not be sequenced, only the regions directly adjacent to it (the primer regions) which are used to define the target region.
After the PCR process is completed, the products of the reaction are put in an agar gel and subjected to an electrical field. The molecules will migrate various distances through the gel based on size, shape and electrical charge. The gel is then stained with a fluorescent DNA stain so that the molecules can be seen. Each PCR reaction is designed to produce DNA molecule copies that will all be of the same specific size and that size can easily be determined from the gel.
If the target material is found and copied, the dye fluoresces and gives an image of the DNA of the individual.
DNA Test Results
The image above is for various DNA targets. In the case of DNA testing for prcd-PRA & FN the results will look like this (only one mutation is tested for!):
prcd-PRA or FN DNA Test Results
DNA testing can accurately detect gene mutations responsible for disease (where the mutant genes causing the disease have been located in the canine genome) and for coat colour testing.
When DNA testing for coat colour, each colour gene is tested for separately. For example, in a black cocker suspected of carrying for red (a recessive gene) the result will look like this:
DNA Coat Colour Results
If a solid black dog is dominant for black there will be no hidden recessive colour, his DNA target will look like this:
DNA Coat Colour Results