A basic grasp of the genetics of dog breeding is essential if you are interested in being a dog breeder.
Once you understand breeding dog genetics you can use it through selective dog breeding to improve both the vitality and standard of your dogs and to avoid genetic diseases in your pups.
Laws Behind the Genetics of Dog Breeding
Genes come in pairs
Genes are like a program that determines an individual’s appearance and behavior. They are strung together like a paired string of beads to form chromosomes.
To make a pair, you get one gene from mom and one gene from dad
Each of a dog’s cells (except sex cells) contains two strands of chromosomes, one from the father and one from the mother. Sex cells (sperm and eggs) have only one strand of chromosomes.
At fertilization, a sperm and an egg join to form an embryo in which the chromosomes inherited from the two parents are again joined into pairs.
What you see is the result of genes
The genes that are paired along the chromosomes determine the traits of the offspring – what it looks like, and even how it behaves.
However, not all genes that are inherited can be seen in the offspring
An individual may inherit genes that are:
- Unalike in the pairs, in which case one usually “dominates” the other, so that the dominant one shows up in the characteristics of the puppy, and the recessive one is unexpressed and hidden. Such a puppy is said to be genetically heterozygous for the trait coded for by that gene pair.
- The genes may be identical and code for the same trait, which will then be expressed in the offspring unopposed. Such as puppy is said to be genetically homozygous for the trait coded for by that gene pair.
An example: Miniature Schnauzer coat color
Coat color in Miniature Schnauzers can be complicated, but we’ll keep things basic for this example.
A black and silver puppy at front with two salt and pepper litter mates on the top right and two pure black puppies on the top left >>>>>
The gene “B” codes for salt and pepper coat color, the gene “b” codes for a black and silver coat, and “B” is dominant over “b”.
As such, a black and silver puppy will result only if it inherits two copies of the “b” gene, one copy from each of the parent’s chromosomes, so that genetically it is “bb”.
For recessive traits, like black and silver coloring, what you see in the dog is a true reflection of what you got in the genetics.
But if the pup inherits the “B” gene (for “salt and pepper”) from one parent, and the “b” gene (for “black and silver”) from the other the puppy will be salt and pepper colored because the “B” gene (with a capital letter) is dominant over the recessive “b” gene.
And a dog that has inherited two “B” genes – one from each parent – will also be “salt and pepper” colored.
So, by the genetics of dog breeding in Miniature Schnauzers, the “salt and pepper” coat can correspond either to the Bb (heterozygous) genotype or the BB (homozygous) genotype.
A dog’s genetic inheritance is therefore not always fully revealed by its appearance (phenotype)!
To illustrate, this is what you’d get if you crossed a salt and pepper dog that had a black and silver parent (so was carrying the “b” gene for black and silver) with a black and silver bitch.
As you can see, about half the pups would be black and silver, and the other half would be salt and pepper colored.
Using Breeding Dog Genetics in Selective Dog Breeding
Once you know whether a feature or genetic defect is dominant or recessive, you can put chance on your side by planning your selective breeding accordingly.
If you always want black and silver puppies, for example, always use black and silver sires and dams, but if you consider black and silver coat color to be a fault, select salt and pepper breeding dogs and bitches that have no black and silver dogs in their ancestry.
Inherited Diseases and Genetics of Dog Breeding
Because of the high degree of inbreeding inherent in many purebred dog lines, a wide range of genetic defects are overrepresented in such dogs, compared to mixed breed mongrels.
The overwhelming majority of these defects are recessively inherited.
Look at this chart. The recessive gene that codes for a genetic disease is shown in red.
It shows that by the genetics of dog breeding, even very moderate inbreeding (as in this common example of “line breeding” of dogs where a dog is mated to its granddaughter) can result in half a litter being struck with a genetic disease, and the other half carrying it, even if the disease has never been apparent in the breeding line before.
It is well worth doing a little research on the breeds you are considering working with to ascertain the most common issues in that breed – every breed will have something lurking in the genetic pool.
Some of these inherited defects will be lethal before the age of breeding (e.g. portavenal liver shunt) but many only manifest as problems in older dogs.
Normally, problems only arise when two dogs that both happen to carry the same recessive genetic defect are mated together.
By the simple laws of genetics the offspring of such a mating – where both parents carry the fault but are not expressing it (i.e. are heterozygous for it) – have a 25% chance of suffering from the defect.
If both parents suffer from the fault (and are therefore genetically homozygous for it), then 100% of their puppies will be affected.
Out Breeding Dogs
By the genetics of dog breeding or any animal breeding for that matter, when you cross totally unrelated individuals the progeny are imparted with what is called “hybrid vigor”.
While they might not win at the dog shows, they will show higher reproductive performance, strength, resistance to illness, and overall health and vitality than line bred dogs.
They’ll also have a much lower chance of being homozygous for any genetic defects and so tend to exhibit the genetic strengths of both parents.
Genetics of Dog Breeding and Cross Breeding Dogs
Because the parent genetics are so different from each other, “designer” pups that result from cross breeding dog experiments will be even more vigorous, long lived and less likely to suffer genetic defects than their parents could ever hope to be.
Cross Breeding Dog Examples:
Crossing a Miniature Schnauzer with a Cocker Spaniel will produce a genetically stronger cross bred than mating it with a Poodle, because Mini Schnauzers have Poodle in their ancestry so the two are closer genetically than the Mini Schnauzer and the Cocker Spaniel.
How Do I Reduce the Risk of Genetic Defects???
You will find that many dog breeders will malign the stock of other breeders. There is a lot of jealously between breeders, especially those who show their animals and compete with each other.
Some will happily tell you about the congenital defects lurking in the lines of their competitors’ dogs.
Truth be told, all pedigree breeds, simply because they are pedigree (and therefore have a limited genetic pool), will have some genetic disease or other in their lines. It goes with the territory!
Do your research and find out the most common problems in the breed you fancy.
For some genetic disorders, testing of the parent stock is a good screen for possible problems in their progeny (e.g. hip dysplasia). For many others, however, it is not.
However, because most defects are recessive (and so may not be evident in the dog carrying them) just because a dog is not affected, doesn’t mean that its progeny won’t be.
While such practices can have (limited) use in exposing and weeding out undesirable recessive genes in a line, line breeding or inbreeding only “works” if the resulting pups are culled from breeding. Unfortunately most are culled to become people’s pets – with the inherent risk of developing genetic illness. The best insurance is to get a grip on the genetics of dog breeding, and stay as far away from line breeding and inbred dogs as you can!