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by hodie on 16 February 2010 - 23:02
NOTE:
I have stated above, based on what Dr. Kooistra has discussed with me, that the genetic mutation is a unusual type and is a deletion. At the moment, I do not know more about that because this is what his research will discuss. So I look forward to learning more about it.
The bottom line is that we need not throw all carriers out of consideration for breeding, but, given that genetic probability suggests that 18% of the GSD population might be carriers, that is not a small number and it makes good sense to consider testing dogs whom one is considering mating. I think this issue will be clarified somewhat after his research has been clarified because he has on his team people who are experts in the bloodlines known to carry this disorder. Of course, they only know what they have concluded from research and given that there are many bloodlines they have not sampled, the stats could be higher.
It is an interesting topic, but in real life, it is painful for a breeder, for an owner who ends up getting such a pup too early to know it is a dwarf, and certainly for the poor little pups so afflicted. I hope this is of interest and helpful. I do still intend to more carefully explain the genetics of inheritance if anyone is interested as soon as I have time.
I have stated above, based on what Dr. Kooistra has discussed with me, that the genetic mutation is a unusual type and is a deletion. At the moment, I do not know more about that because this is what his research will discuss. So I look forward to learning more about it.
The bottom line is that we need not throw all carriers out of consideration for breeding, but, given that genetic probability suggests that 18% of the GSD population might be carriers, that is not a small number and it makes good sense to consider testing dogs whom one is considering mating. I think this issue will be clarified somewhat after his research has been clarified because he has on his team people who are experts in the bloodlines known to carry this disorder. Of course, they only know what they have concluded from research and given that there are many bloodlines they have not sampled, the stats could be higher.
It is an interesting topic, but in real life, it is painful for a breeder, for an owner who ends up getting such a pup too early to know it is a dwarf, and certainly for the poor little pups so afflicted. I hope this is of interest and helpful. I do still intend to more carefully explain the genetics of inheritance if anyone is interested as soon as I have time.
by hodie on 17 February 2010 - 00:02
Someone asked me a good question. Here is the question and my answer.
Question: Is it possible for two carriers to produce a dog that is not a carrier?
Answer: Yes, it is possible. This is why understanding the Punnett Square can help. In a mating between carriers, in the first generation, on average, 25% of the progeny will be non-carriers, 25% will be affected with the condition, and 50% will be carriers. This is an approximation, so it is possible that you might hit the jackpot and end up with no carriers, or no affected progeny, but unlikely. For example, in a litter of 8, you might have one with the condition, or three, or more. That is higher than 25%.
In the second generation, these percentages go up for having an affected progeny. But, in autosomal recessive conditions, the disorder is not typically seen in every generation. This is a huge part of the problem because people don’t see it, and then suddenly, there it is. This is in contrast to autosomal dominant disorders which generally occur in every generation of an affected pair of mates.
If one parent is not a carrier bred to a carrier, you get, in the first generation, about 50% carriers and 50% non-carriers, but you cannot have an affected pup.
Question: Is it possible for two carriers to produce a dog that is not a carrier?
Answer: Yes, it is possible. This is why understanding the Punnett Square can help. In a mating between carriers, in the first generation, on average, 25% of the progeny will be non-carriers, 25% will be affected with the condition, and 50% will be carriers. This is an approximation, so it is possible that you might hit the jackpot and end up with no carriers, or no affected progeny, but unlikely. For example, in a litter of 8, you might have one with the condition, or three, or more. That is higher than 25%.
In the second generation, these percentages go up for having an affected progeny. But, in autosomal recessive conditions, the disorder is not typically seen in every generation. This is a huge part of the problem because people don’t see it, and then suddenly, there it is. This is in contrast to autosomal dominant disorders which generally occur in every generation of an affected pair of mates.
If one parent is not a carrier bred to a carrier, you get, in the first generation, about 50% carriers and 50% non-carriers, but you cannot have an affected pup.
by Mark3 on 17 February 2010 - 23:02
Thank you for your time in putting this together Hodie, very educational posts.
by missbeeb on 18 February 2010 - 06:02
I'm very interested, Hodie! I find your posts so much easier to digest. I will print them off to keep.
Thank you!
by AmbiiGSD on 18 February 2010 - 07:02
Thanks for Posting the article Hodie.
It's too early for me to take it in, so I'll have agood read later when I'm awake.
It's too early for me to take it in, so I'll have agood read later when I'm awake.
by bazza on 18 February 2010 - 08:02
As usual Hodie very informative helpful well put together post. Thank you, definately one to copy and keep.
by Sue B on 18 February 2010 - 12:02
Hi Hodie,
Thanks for sending the entire article to me via email attachment. Most appreciated.
Best Regards
Sue
Thanks for sending the entire article to me via email attachment. Most appreciated.
Best Regards
Sue
by hodie on 29 April 2010 - 22:04
BUMP FOR TOPICS UNDER GENERAL FORUM
by Sunsilver on 30 April 2010 - 15:04
This is a reply to AmbiGSD, and others who are afraid we might be losing something valuable from the GSD gene pool if we breed to eliminate dwarfism.
The defective gene is the result of a deletion. This means a section of the DNA in the chromosme, specifically the part that codes for normal function of the pituitary gland is MISSING. I cannot possibly see how eliminating this defective gene from the gene pool is going to have any effect on other desirable healthy genes. It is a simple mistake in the genetic code, that could be compared to having a couple of words missing from a sentence. The missing words affect the pituitary gland ONLY, nothing else.
As the number of carriers in the GSD gene pool for this gene is quite large (around 18%) if we don't breed these dogs, yes, we DO stand to lose a lot of variability from the gene pool
The sensible thing to do would be to TEST the sire and dam before mating, to make sure both of them are not carriers. This way, we could eliminate dwarf pups, without seriously affecting the size of the gene pool. If my bitch were a known carrier, I would make sure I did this before breeding. If I were being really ethical, I would also warn puppy buyers that the pups had the potential to be carriers, and they should have blood tests done before breeding.
As very few people REALLY understand genetics, this means I'd probably be stuck with a bunch of unsellable puppies....
The defective gene is the result of a deletion. This means a section of the DNA in the chromosme, specifically the part that codes for normal function of the pituitary gland is MISSING. I cannot possibly see how eliminating this defective gene from the gene pool is going to have any effect on other desirable healthy genes. It is a simple mistake in the genetic code, that could be compared to having a couple of words missing from a sentence. The missing words affect the pituitary gland ONLY, nothing else.
As the number of carriers in the GSD gene pool for this gene is quite large (around 18%) if we don't breed these dogs, yes, we DO stand to lose a lot of variability from the gene pool
The sensible thing to do would be to TEST the sire and dam before mating, to make sure both of them are not carriers. This way, we could eliminate dwarf pups, without seriously affecting the size of the gene pool. If my bitch were a known carrier, I would make sure I did this before breeding. If I were being really ethical, I would also warn puppy buyers that the pups had the potential to be carriers, and they should have blood tests done before breeding.
As very few people REALLY understand genetics, this means I'd probably be stuck with a bunch of unsellable puppies....
by hodie on 30 April 2010 - 18:04
This was all explained before in the voluminous posts on this thread and was resurrected because of the threads on the other side of the forum. Some of those posts contained incorrect information. None of the other threads on this same subject in many years have ever been as thorough as this one, but a lot of people did not bother to read it because it was in Ireland.
The issue some had in this thread was that a defective gene might still be paired with a gene that was required for something else. Is that impossible? No, but it is not likely. The defect is, in fact, a simple missing amino acid. This mutation clearly occurred years ago, probably a random occurance (this happens very frequently in genes but often has no import). The researchers know the bloodlines involved and also know where this deletion first occurred. However, until the journal article is published, we can speculate all we want. The rate of carriers might be higher in fact than the 18% that Dr. Kooistra has calculated, or it could be lower, but that is unlikely.
What is clear is that the cause for a SPECIFIC type of drawfism involving the pituitary gland has been discovered. It exists not only in GSDs by the way. There are also other causes for dwarfism, or severe growth retardation. Hopefully the paper will be published in the next few months. I expect a copy of it when it is and will post a link to it. In the meantime, it is advice falling on deaf ears that all breeders could learn more about genetics and could send away a test tube of blood to be tested. But, until the test is available in the US, it is unlikely to happen very frequently. Even those breeders in Europe who could more easily do this have not rallied to it. Why? The answer is obvious. Because people do NOT understand genetics at all, saying a dog carries this genetic defect would be a death knell for a breeding program using such a dog. That in itself is sad, because it belies the issue and how to solve it correctly.
The issue some had in this thread was that a defective gene might still be paired with a gene that was required for something else. Is that impossible? No, but it is not likely. The defect is, in fact, a simple missing amino acid. This mutation clearly occurred years ago, probably a random occurance (this happens very frequently in genes but often has no import). The researchers know the bloodlines involved and also know where this deletion first occurred. However, until the journal article is published, we can speculate all we want. The rate of carriers might be higher in fact than the 18% that Dr. Kooistra has calculated, or it could be lower, but that is unlikely.
What is clear is that the cause for a SPECIFIC type of drawfism involving the pituitary gland has been discovered. It exists not only in GSDs by the way. There are also other causes for dwarfism, or severe growth retardation. Hopefully the paper will be published in the next few months. I expect a copy of it when it is and will post a link to it. In the meantime, it is advice falling on deaf ears that all breeders could learn more about genetics and could send away a test tube of blood to be tested. But, until the test is available in the US, it is unlikely to happen very frequently. Even those breeders in Europe who could more easily do this have not rallied to it. Why? The answer is obvious. Because people do NOT understand genetics at all, saying a dog carries this genetic defect would be a death knell for a breeding program using such a dog. That in itself is sad, because it belies the issue and how to solve it correctly.
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