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Genetics for Dummies |
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An Introduction |
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This is the first chapter of the Collieinfo course of genetics for dog lovers. Much of the texts that will follow is from the writings of Dr. P-E Sundgren, geneticist, former Advisor to the Swedish Kennel Club, published here with his permission. The articles may be read in unabridged version (in Swedish) on Dr. Sundgren´s website www.genetica.se What Dr. Sundgren says applies to all dog breeds. We serve up the text in shorter chapters and when needed will put in comments of our own, relating to Collies. Our comments will be marked by different lettering, or different colour print, as in, Dog breeds were created first. Modern genetics second. That is, the breeds were started by people who did not quite know what they were about and couldn´t foresee the consequences. ”Many dog breeds have a very ancient background of development. There is historical evidence that dog races, with looks roughly like those of today´s dogs, have been around for hundreds or even thousands of years. /…/ Ideas about the importance of pure-breeding for the quality of an individual animal grew considerably stronger during the late 19th century and the first third of the 20ieth century. That was the foundation for highly restrictive rules for breeding, with closed stud books for populations which were often based on just a small number of individual animals. Show- ring competition, based on the concept of breed, began in earnest towards the end of the 19th century and created the basis for intense selection for certain conformational criteria, resulting in breeding being concentrated to few individuals. As a result of this change in conditions for the breeding of animals, the increase in inbreeding in many races of pet animals during the 20ieth century has progressed at a rate that was neither on the agenda nor even possible in early times.” (Genförluster hos sällskapsdjur – ett hälsoproblem?/ Genetic loss in pet animals – a health problem? Sundgren s1 Translation by website editor) How were the modern dog breeds set up? A group of fanciers selected a type of dog which they liked. Then they sat down at a table and agreed on a “standard” – a template – for how the Dog should look. Not the dogs – the Dog. The prototype. Then they set about competing each other for who was to be the best producer of it. Of course they inbred. There is no other way if you want to punch the Dog out from a group of actual dogs, with each individual one having its own curve of tail, its height, its coat colour or its own setting of ears. What the early breeders didn´t know was this. Every one of the dogs which they picked carried at least four or five defective genes. Everybody does, humans as well as dogs, but most of us have single versions of those genes only and so are both unafflicted and happily unaware of them. But once you start doubling alikeness by breeding father to daughter, or full sibs to each other, and then go on “breeding pure” the desired traits by carrying on with inbreeding…then you will, by necessity, eventually breed pure the defective genes as well. And when you close the stud book, it´s no longer possible to bring in new dogs, with new genes. You´re stuck with the genes you have and must continue to breed them. Now if you wish to start a new breed, that is how you must begin. But if you want to carry on breeding within a closed studbook, you must either know basic genetics; or be willing to listen to those who do. Many traditional breeders neither knew nor would listen. When basic genetic rules at last started getting through to unwilling ears, the terms that stuck were those which predicted what could be expected from the next mating and the next litter. Dominant, recessive and polygenic traits. Recessive traits go like this: I have one single gene, that whispers faintly about blue. So blue eyes I won´ t have. But if I have two genes, whispering in chorus, then – and only then – will I have blue eyes. The recessive gene needs a mate exactly the same in order to make itself heard. Dominant traits go like this: I have one single gene, that says BROWN EYES in a loud voice. That´s enough, brown eyes I will have, even if I should happen to have a second gene along with it, whispering blue The dominant gene makes itself heard on its own and silences the recessive one. Polygenic traits are those which add up. They go like this: I have one gene from my mom, saying Grow tall! And two from my dad, saying the same. So with only three genes for height, I´m five foot two. My daughter, having two genes for height from me and four from her father, is a splendid five foot eight. Breeders learnt this stuff because it was of interest to them. They knew what to expect from the next litter. Coat colours are often inherited in this fairly simple manner. In the Collie, the blue merle colour is dominant, meaning that an average of fifty per cent of the puppies in a litter with a merle dam or sire will be merle. The tricolour coat is recessive, so two Collies of that colour can only produce tricolour pups between them. Dysplastic hips are polygenic in all dog breeds, as is size, and therefore a bit more difficult to predict. But all breeders know that if you breed two large Collies to each other, the puppies will certainly differ in size – but will tend to be above average in height.
Unfortunately, there was one term that didn´t
catch on at all. And even more unfortunate was the fact that it
happened to be the one term you must be aware of, if you breed
animals with a closed stud book.
This is the one concept that breeders of purebred dogs need to know.
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