The genome for the domestic dog was mapped in 2004 and released across biomedical, pharmaceutical and veterinary platforms, this eventually gave rise to dog DNA tests, so how do dog DNA tests work?
This is an answer that requires some in-depth explanation, read on and unlock the mysteries of Doggy DNA!
What is DNA?
Deoxyribonucleic acid – the remarkable double helix that contains the key to life. Nucleotides on each side with bases: Adenine, Thymine, Cytosine and Guanine (A-T, C-G). The double helix was identified in 1952 by Rosalind Franklin using X-ray Crystallography along with Maurice Wilkins, and James Watson and Francis Crick described the hypothesis of the DNA structure. The three went on to win a Nobel Prize, Rosalind passed away four years before this. From the ’50s onwards DNA became a hot topic and more research funding.
DNA is made of sugar (deoxyribose), phosphate group where together they function as the ‘backbone’ and the nitrogen base, which connects to its opposite, complementary base.
Adenine and Thymine are complementary base pairs, as are Cytosine and Guanine. They just go together! The sequence of the base pairs determines what genes are expressed. Gene expression is when a protein is produced and can be as small as 1000 bases or 100,000,000!
DNA is the blueprint for all the processes such as cell division, cell regulation and cell metabolism. The genes controlling physical appearance is about 1% of the whole genome.
The instructions we keep going on about are for the synthesis of proteins. Hormones, enzymes, antibodies are all proteins! These complex proteins help manage the system on a larger scale, such as providing adrenaline when running from a predator, or releasing oxytocin in the brain when bonding with your newborn.
Moving on, if a dog wore jeans, would it be worn on the back legs or jeans covering all the legs?
Genes, DNA, chromosomes! It’s all so confusing! I will explain below how they all tie together.
Genes are the smallest part of the puzzle. There can be several genes that control say, fur colour, for example. Genes are found in areas of the DNA. Dogs have specific slots in their DNA that can be seen across the species (four legs, tail) which can be matched and used as evidence when building a genomic profile. Some dogs have different slots that are filled with specific genes, not seen in other breeds such as a Shar-Pei’s wrinkles. Particular genes can also be found on chromosomal locations.
Gene located in a small section of DNA >
DNA is tightly coiled and packaged up with a few extras, into a chromosome >
Chromosomes come in pairs, except in sex cells as dogs ovum and sperm carry one copy of the sex chromosome. So momma pup will pass on the X chromosome, and the sperm can deliver an X or Y.
Overall, a dog has 39 chromosomes, in comparison to a human who has 46 – including sex chromosomes respectively.
The chromosomes can be seen in the nucleus of a cell using an electron microscope; anyone recall mitosis… cell division makes chromosomes more visible under a light microscope.
To recap, smallest to largest:
Gene > DNA > Chromosome > Cell Nucleus
Genes: Dominant and Recessive
Breeders can select certain dogs to maintain a desired trait, such as the ‘blue’ colour seen in some French Bulldogs and Staffordshire Bull Terriers. This requires close maintenance of bloodlines and a strong understanding of genetics. Here are some terms and their definitions:
Allele (Ahh – Lel) – one or more alternative form of a gene
The prefix: Homo = Same, in Ancient Greek. Homozygous (ho-moe-zi-gus) – two copies of the same gene
Heterozygous (heh-terr-oh-zi-gus)– two copies of the gene are presented by different alleles
Genotype (Gene-oh-type) – set of genes inherited from the parents
Trait (Tray-ate) – a physical, physiological or behaviour that has been expressed (desirable blue coat)
Phenotype (Feen-oh-type)– Displaying the trait (puppy has inherited blue coat). The phenotype can also refer to behaviours, biological mechanisms and so on
Like humans, dogs produce melanin which gives features their colour. Using a Punnett square, as seen above, we can use the parent dogs’ genetics to determine the puppies coat.
Punnett squares are a handy method for looking at dominant and recessive genes, to work out the likelihood of a trait being expressed (phenotype) It can get confusing, so colour coding is beneficial in my opinion! Here is one I made based on two Black Labradors, with an explanation down below:
We have an allele – B, which is a dominant fur colour gene, it has the power to switch off recessive genes or overpower the recessive expression, which is why BB, Bb alleles will produce black coats.
Allele bb – is the recessive copy of the gene. For a Labrador to have a chocolate brown coat, it must have alleles bb.
Homozygous gene example (Same allele) – bb
Heterozygous gene example (alternative alleles) – Bb
The ‘e’ alleles are responsible for the yellow coat. The recessive ee gene can override the B/b genes due to a mutation. When there is a dominant allele ‘E’, the coat colour is determined by the B genes. It’s quite confusing and maddeningly interesting.
So, how does this information fit into dog DNA tests?
Dog DNA tests differ from human tests because they only go as far as the great-grandparent, whereas human DNA can be traced back many generations. Autosomal DNA markers (a pair of chromosomes) are used which presents the genes seen across both pupper parents and their lineage.
Genetic markers are a known location on a chromosome. This is achieved through ‘gene mapping’, a painstaking effort to determine where a specific genes’ alleles reside on a chromosome in a fixed position. There will be known locations across breeds, that detail height, for example. Using similarities, differences and mutations across the doggy genome, scientists were able to find sites that were unique to specific breeds and commonalities across canines.
A single nucleotide polymorphism (SNP) is an example of a genetic marker. It’s kind of like a buffer between genes, they occur every 1000 bases or so, which means an individual could have 4 million SNP’s across their whole genome. Some of these SNP’s have become critical in the study of genetics; using SNPs has helped advances in pharmacology, as some dogs cannot tolerate certain medications and genetic counselling on the risk of developing particular diseases. A typical test is for German Shepherds to make sure they do not have/develop or pass on hip dysplasia, as they are prone to this condition. It is a condition that is heavily affected by environmental factors, such as excessive exercise as a pup or over-feeding.
The entire canine autosomal genome reported over 4000 SNP’s using a variety of breeds to give a vast database in which dog DNA tests can be checked against! The actual laboratory work uses a surface where the SNP’s can attach to by covalent bonding, usually on a glass slide. The samples containing your puppers DNA gets chopped up into manageable pieces, bonds with a fluorescent dye (green) and added to micro-array, which is essentially the basis of a computer chip! The control sample has a red dye. When the sample matches with a gene, that marker will fluoresce and will be scanned by the computer for analysis.
These chips are super fast, easy for labs to use, the computer scanning and algorithm reduces the window for human error when analysing the results. Tests are over 95% accurate, and quality assured.
Test uses and reports
Depending on what tests you chose for your dog, the report will be catered to that test. Generally, lineage is broken down into a pie chart. A mixed-breed dog could present with a large percentage of one breed’s genetics, and a smaller breakdown across 2-4 other breeds. The smaller portions don’t usually have much of a bearing when it comes to lineage.
In regards to health, the test can screen for genes that breeds show a predisposition for such as hip dysplasia, deafness and cleft palate formation. This is an excellent way to make sure dogs used in breeding are not carriers of genes that would negatively impact their pups quality of life or their puppies owner. The medical costs or loss of a pet can be devastating; genetic testing is a wonderful way to prevent genetically related conditions from being passed on. The ancestry of mixed breeds is super interesting, but also informative for staff at a rescue shelter who are trying to get their canine residents a forever home!
There are various price points across the internet, catered to your needs. Make sure to use a lab that is working with genetic institutions and veterinarians to ensure accurate results and consultations, and some laboratories are not regulated. See our article on ‘Can a DNA test tell a dogs age?’ for some more information on test kits, and instructions for acquiring a decent DNA sample.
What percentage of a breed makes a dog a ‘pure-bred’?
The percentage must be over 87.5% for the dog to be considered a pure-bred. This refers to their lineage, which has been monitored closely and yields information on future generations reliability and predictability in regards to health and behaviour. You can see pure-bred dogs at events such as Crufts!
References:
https://www.akc.org/expert-advice/dog-breeding/genetics-101-part-3-of-a-series/
https://www.animalgenetics.us/canine/canine-color/ELocus.asp
http://www.doggenetics.co.uk/dilutes.html
https://www.genome.gov/12511476/2004-advisory-dog-genome-assembled
https://www.genome.gov/about-genomics/fact-sheetshttps://www.genome.gov/about-genomics/fact-sheets/Deoxyribonucleic-Acid-Fact-Sheet
https://www.genome.gov/about-genomics/fact-sheets/DNA-Microarray-Technology