THE ART OF BREEDING GREAT DANES OR,
TO BREED OR NOT TO BREED...
[Excerpt from The Great Dane, Model of Nobility, by Jill Swedlow]
PART IV
When gametes (sex cells) are formed, they contain only 1/2 of the genetic make-up of each parent. One gamete may end up with the gene which causes brindle stripes, and the other gamete may carry the other gene for fawn body color. The same will be true of the male’s sperm cells. It is pure chance as to which of the bitch's ova becomes ripe first and ovulates into the fallopian tubes to await the dog's sperm. It could be ones with the fawn gene or ones with the brindle gene. Since there are an equal number of each, there is a fifty-fifty chance of it being either. The same holds true of the dog's sperm. Approximately one half of the millions of sperm contained in each ejaculate carry his fawn gene, and one half carry the brindle gene. If the sperm which fertilizes the ova carries a gene for fawn, and the ova has the gene for brindle, the pup will be born brindle since brindle is dominant to fawn. The resulting pup will carry one gene for brindle and one for fawn and is, itself, genetically capable of producing get of either color depending on the genetic make up of its mate. If the bitch's ovum happens to be one with the gene for fawn, and so is the dog's sperm, the pup will be fawn and carry two genes for fawn. If the bitch's ova carries the brindle gene and so does the dogs sperm, the pup will not only be brindle but will carry brindle in a double dose (both genes brindle, eg.
homozygous) and can NEVER produce any get except brindle since brindle is dominant to fawn.
The laws of probability tell us that with animals carrying simple recessive and simple dominants, the chances are always 50-50 as to which gene is inherited by the pup. The calculations are over the expectancy of 100 offspring so if your brindle dog has been bred to 3 fawn bitches and has produced 15 brindle pups, there is STILL a 50-50 chance that the next litter he sires could contain fawns. A small chance, but still a chance. This will also tell you something about his genotype. You
know he carries a recessive gene for fawn because he has produced fawn pups even though he is himself brindle. You also know that he carries the dominant brindle gene because he
is brindle.
Sometimes semantics seem to be responsible for some misunderstand­ing. One breeder once asked me why her brindle dog sometimes produced fawn pups instead of always producing brindle pups if the brindle gene was dominant. She didn't understand that the gene
had to be passed along to the pup (inherited) in order for it to be able to exert its dominance. The chances of the brindle gene being passed along, when the dog carries a recessive gene for fawn also, is 50-50. Only dogs that are homozygous for the brindle gene (they have 2 genes for brindle and carry
no gene for fawn) will produce 100% brindle pups.
Admittedly the above examples are overly simplified when compared to multi-genetically controlled traits. There are other types of genes which behave in different ways. In order to predict the expectancy of certain traits accurately, you must have a pretty good idea of the mode of inheri­tance.
The example of canine coat color can be translated into many traits of Great Danes. Brindle is dominant to fawn but there are other colors (and patterns) in the breed which are not quite so simple to understand and predict. The relationship between genes, which is dominant to which, and which are recessive, can be likened to a pecking order among chickens. The rooster (most dominant gene) is at the top of the heap and bosses everyone around. Next is the bossiest hen who only takes orders from the rooster. Below her are the rank and file of her subordinates, all of whom obey their betters, and in turn, control their underlings until you come to the bottom of the heap and find the little hen (most recessive gene) whom everyone picks on. She never gets to eat or express herself until she is the only one in the barnyard.
Now you are probably beginning to wonder how any of this can be helpful since little is known of the mode of inheritance of many canine traits. Also, few traits are controlled by a single gene. Most are multi-gen­etic, such as head shape. There are probably thousands of genes and their modifiers which make up the blueprint which determines the shape of a dog’s head. Although it would be very difficult, not to mention impractical, to try isolating each gene and how it behaves in creating the overall blueprint, these controlling groups of genes often tend to act in recessive or domi­nant ways as a group. For instance, let us say you have a dog with a beautiful head. You mate him to 10 bitches whose head type ranges from ugly to plain, but none are gorgeous. If 75% of the offspring have beautiful heads like their sire, you can be fairly accurate in concluding that your dog is dominant for his head type. This can be applied to any conformation trait or group of traits which tend to occur in the same manner. But what about traits which, as a group, behave in a recessive manner? Since recessives are masked by dominants, they can be difficult to isolate. (The recessive genes often control undesirable traits such as an undershot jaw or light eye color).
We will use an undershot jaw (the lower teeth protrude forward of the upper) as our example. Assume you breed a bitch and dog to each other who both possess a correct bite. Some of their puppies are undershot. What does this tell us? It is highly probably that
both parents are carriers of the recessive gene, or genes, which produced the bad bite. (Remember the brindle dog and bitch who both carried fawn recessively and produced a fawn pup?) We are dealing with the same principle here. What makes a trait like this difficult to breed out is it's recessive nature. Their pups could as easily have had a correct bite but still carried the genes for a bad bite recessively. (See Illustration #?). These recessives can be masked by their dominant alleles (genes which appear on a common location on the chromosomes) for generation after generation until the time when they pair with another like recessive and express themselves in the puppy’s phenotype. If you will refer back, once again to chart #?, you will see that there is a 50% probability that an offspring of recessive carrier parents will itself be a carrier.
This is a rather sobering thought, especially when one realizes that such recessives can skip generations and the individual must be test bred in order to ascertain if it is, indeed, a carrier. So what is the logical solution to this problem? Intelligent breeding practices and ruthless culling, which will be discussed later.
There are several different methods of planned breeding used by knowl­edgeable breeders. All have their good points and their drawbacks. Sometimes one must simply experiment with the different methods to establish which will work best under any given circumstances. This, then, brings us to a discussion of inbreeding, linebreeding, and outcrossing.
Copyright 2002, Jill Swedlow. Sunnyside Danes. All rights reserved
