Quite a while back I started a series on genetics, you can find the first post here, so to pick up where I left off…a puppy receives 50% of it’s genes from the sire and 50% from the dam. There is no way to know what half they will get or to control that so responsible breeder’s try to breed dogs that are good specimens of their specific breed. This means dogs that are good representations according to their breed standard; you should study and know your breed standard. With my breed we do many health clearances before breeding, however with that being said you can do your very best at choosing a stud dog or dam and some of the pups in a litter will be better than others. You may also get some recessive genes pop up or threshold traits that account for certain diseases. When I did my breeding I did health clearances on Riva and I looked for that in the stud dog also, however clearances alone are not my deciding factor on breeding two dogs. I believe that the health clearances are to be used as a tool to help in the decision process and that looking at the WHOLE DOG, it’s ancestors and their offspring (progeny) in the first 2-3 generations is where the decision should be made on who I breed. I have read various articles on genetics and attended a wonderful seminar given by Claudia Orlandi on The ABC’s of Dog Breeding and also her seminar on Practical Canine Anatomy and Movement. This was a fantastic experience and I highly recommend both of these home study programs whether you are a breeder or not. Another good resource I have read on diversity, and this relates to Chesapeake’s, however the information transcends over to other breeds as well is located here
So on with the lesson…I thought I would talk about additive genes as they apply to polygenic traits (traits controlled by more than one pair of genes) today. An additive gene refers to such things as movement, forequarter and hindquarter angle, temperament, hunting ability, just to name a few. The better additive traits a dog has the more likely it carries good genes for that trait and the better chance it will pass these good genes on to the offspring. So in essence what you see on a dog is a good indication of what the dog will produce. This is a great help from a breeding stand point because you don’t have to guess what you are going to get because “what you see is what you get”! So if a dog has bad angles it is likely to pass that on to the offspring. For example one of the many things I looked at in a male was a good shoulder, I did not want to loose the good shoulder Riva has because that happens to be one of the traits that is hard to correct.
Additive traits also play a role in threshold traits which are linked to cryptorchidism, hip dysplasia, cardiomyopathy, luxating patellas, infertility, to name a few. It takes several genes to influence a threshold trait, the genes come from both the sire and dam but may not be in equal numbers from each. The threshold trait will not show itself in the dog unless a critical number of genes are inherited. It is a “all or none” additive effect, the dog either is or isn’t! For example if it takes 8 undesirable genes to produce cryptorchidism, a puppy who gets 5 from the sire and 3 from the dam will be cryptorchid but if the pup gets 4 from the sire and 3 from the dam they will not be cryptorchid because they have not reached that critical number, (threshold) of genes. Most threshold traits are associated with defects and are looked at as recessive traits. From a breeding stand point this is particularly challenging because the given puppy example carries a high number of the cryptorchid gene so if bred to a dog who also has cryptorchid genes the risk is higher of producing cryptorchid pups in the litter.
So I hope this was informative, it’s a lot to think about and just plain fascinating! I will try to get the next genetic post up much sooner.
Reference: Orlandi, C., ABC’s of Dog Breeding