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<blockquote data-quote="Mark Reynolds" data-source="post: 1807523" data-attributes="member: 43196"><p>Genetics Lesson:</p><p></p><p>I am not intimately familiar with each of the genetic defects above. However, most (and by most I mean like 95-99.99%, but I don't have known percentages) are the result of the the animal (or organism(could be a plant)) ending up with 2 RECESSIVE genes, 1 from each parent. These recessive genes are rare in the general population. However, the recessive genes, when present, are present in half the offspring that originate from the parent. So.......If you have an animal that happens to have a recessive gene for a genetic defect (BTW, when a recessive gene is paired with a DOMINANT gene for the same trait, you only see/experience the effect if the dominant trait) and you breed it with another animal from the general population (where the recessive gene is rare) there is a very low chance of the offspring ending up with 2 recessive genes. When an animal ends up with 2 recessive genes for the genetic defect, there is no dominant gene present to mask or prevent the genetic effect from being expressed, and the animal ends up with the genetic defect or condition. In line breeding or inbreeding, you are mating siblings that each have a 50/50 chance of being a recessive gene carrier which means there is a 12.5% chance the progeny will end up with 2 copies of the recessive gene and will have the genetic defect. If you breed offspring (likely a cow/heifer) to a parent (likely a bull), it is a 'given' that the bull/parent is a carrier of the recessive gene and a 50/50 chance the parent's offspring being bred to the parent also carries the recessive gene. There is a 25% chance that their progeny will have 2 recessive genes for the defect and will therefor suffer from or express the genetic defect. There are tests that can be conducted for the presence of recessive genes for some defects and expression of the defect is simply avoided by not breeding that animal or by breeding it with an animal that tested negative for said genetic defect. I doubt there are tests for every single recessive gene that exists, so complete avoidance of genetic defects manifesting themselves is impossible. Careful review of pedigrees is the best avoidance measure, but it is far from foolproof.</p></blockquote><p></p>
[QUOTE="Mark Reynolds, post: 1807523, member: 43196"] Genetics Lesson: I am not intimately familiar with each of the genetic defects above. However, most (and by most I mean like 95-99.99%, but I don't have known percentages) are the result of the the animal (or organism(could be a plant)) ending up with 2 RECESSIVE genes, 1 from each parent. These recessive genes are rare in the general population. However, the recessive genes, when present, are present in half the offspring that originate from the parent. So.......If you have an animal that happens to have a recessive gene for a genetic defect (BTW, when a recessive gene is paired with a DOMINANT gene for the same trait, you only see/experience the effect if the dominant trait) and you breed it with another animal from the general population (where the recessive gene is rare) there is a very low chance of the offspring ending up with 2 recessive genes. When an animal ends up with 2 recessive genes for the genetic defect, there is no dominant gene present to mask or prevent the genetic effect from being expressed, and the animal ends up with the genetic defect or condition. In line breeding or inbreeding, you are mating siblings that each have a 50/50 chance of being a recessive gene carrier which means there is a 12.5% chance the progeny will end up with 2 copies of the recessive gene and will have the genetic defect. If you breed offspring (likely a cow/heifer) to a parent (likely a bull), it is a 'given' that the bull/parent is a carrier of the recessive gene and a 50/50 chance the parent's offspring being bred to the parent also carries the recessive gene. There is a 25% chance that their progeny will have 2 recessive genes for the defect and will therefor suffer from or express the genetic defect. There are tests that can be conducted for the presence of recessive genes for some defects and expression of the defect is simply avoided by not breeding that animal or by breeding it with an animal that tested negative for said genetic defect. I doubt there are tests for every single recessive gene that exists, so complete avoidance of genetic defects manifesting themselves is impossible. Careful review of pedigrees is the best avoidance measure, but it is far from foolproof. [/QUOTE]
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