Quote:
Originally Posted by mijke
But maybe I am wrong! So please Ina, correct me when there are other reasons why they need more Csw’s for validation.
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HD is for sure caused by several genes, that has to be so because there are more than one bone involved in the joint and there are different forms of causes of HD (to small Caput femoris, to low Norberg degree and so on). Though it is no longer discussed that HD is a genetic desease there are factors like too much training or too highly energetic food in the growth period that have a great influence on the severeness of the genetic caused desease.
So there is not only one reason or one gene mutation that has to be found but very likely the combination of genetic factors that is the reason, at least several different genes. That of course makes research much more difficult, takes much more time and dogs.
Anyway every genetic test that has been validated on one breed has to be checked on every new breed because there are defects with identical symptoms but caused by different mutations. But when you already have one working test you look in every new breed if the genes for the defect are the same or not. If you look for one mutated gene like in the dwarf test you only need one dog, if you look for different genes like in polygenic defect like HD you need more dogs because one dog with HD E may show a defect on the genes 1+3 and the other on 2+4 (just as an example, I am not that far in detailes about this test), or the combination of 1+4 causes severe HD, the combination of 1 + 2 doesn´t.
So as far as I understood they only need 24 dogs to check if they show the same mutations but about 200 to validate a working test.