Inherited disease tests for the Labrador Retriever - DNA
All breeders want to produce animals unaffected by disease.
Most also realise it is important to keep the gene pool as wide as possible.
Currently all DNA tests on the market for Labradors are for autosomal recessive traits and give one of three results.
All breeders want to produce animals unaffected by disease.
Most also realise it is important to keep the gene pool as wide as possible.
Currently all DNA tests on the market for Labradors are for autosomal recessive traits and give one of three results.
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CLEAR
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Two copies of the desired gene. The animal will not be affected by the disease and is incapable of passing on the disease.
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CARRIER
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One copy of the desired gene and one copy of the undesired gene. The animal will not be affected by the disease - can safely be bred from to tested clear animals.
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AFFECTED
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Two copies of the undesired gene. The animal will be affected by the diseases (subject to age of onset) - can safely be bred from to tested clear animals. ALL PROGENY WILL BE CARRIERS but will not be affected by the disease.
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As numerically the largest breed in the world, Labradors are a perfect breed for commercially minded researchers to develop genetic tests for rare problems and then a temptation arises to test and claim clear status when it would be nigh on impossible to be anything other than clear.
In 2010 it became apparent that many DNA tests for Labradors were coming onto the market; some of the tests are for problems where the mutation frequency in the breed is extremely low and this has been taken into account when Breed Council ratified a chart developed by Anne Taylor and myself. This chart is now accepted by The Labrador Breed Council in the UK as best advice in the current light of knowledge. Anne and I try to keep this updated at least once a year.
In 2010 it became apparent that many DNA tests for Labradors were coming onto the market; some of the tests are for problems where the mutation frequency in the breed is extremely low and this has been taken into account when Breed Council ratified a chart developed by Anne Taylor and myself. This chart is now accepted by The Labrador Breed Council in the UK as best advice in the current light of knowledge. Anne and I try to keep this updated at least once a year.
| inherited_tests_for_the_labrador_2012_updated_6.12.2012.pdf |
A further complication with regard to testing within the breed, is the arbitrary split between work and show lines. Some tests are for diseases that had never been seen in certain lines. A good example of this is CNM, which the original researchers traced back to a mutation in a working bred dog. The advice in the above chart takes into consideration the mutation frequency in the different areas of the breed.
A targeted DNA test of a specific disease discriminates genetically normal, carrier and affected dogs from each other and helps breeders optimise their breeding plans.
It is sufficient that one parent in any mating is clear of a particular problem as this will mean the offspring are not affected by disease/problem.
Many kennel clubs and breed associations have made DNA testing an integral part of the breeding programmes, as systematic assessment helps breeders to monitor and reduce the incidence of the inherited diseases; or even eradicate them from the populations while maintaining the necessary genetic diversity for the breed to stay healthy.
A targeted DNA test of a specific disease discriminates genetically normal, carrier and affected dogs from each other and helps breeders optimise their breeding plans.
It is sufficient that one parent in any mating is clear of a particular problem as this will mean the offspring are not affected by disease/problem.
Many kennel clubs and breed associations have made DNA testing an integral part of the breeding programmes, as systematic assessment helps breeders to monitor and reduce the incidence of the inherited diseases; or even eradicate them from the populations while maintaining the necessary genetic diversity for the breed to stay healthy.
Background
- A dog has 39 chromosome pairs including 38 autosomal chromosome pairs and sex chromosomes (X female, Y male).
- One of the chromosomes comes from the dam and one from the sire.
- The genes exist in the DNA strand which is packed into the chromosomes.
- Genes are not passed from generation to generation in isolation, chromosomal crossover means that genetic recombination between paired chromosomes occurs. This results in the production of a new combination of alleles. Genes that typically stay together during recombination are said to be linked. One gene in a linked pair can sometimes be used as a marker to deduce the presence of another gene.
- It is important to note that in that in trying to remove an undesired gene breeders may be removing closely linked desirable genes too. If breeders fall into the trap of breeding from only DNA tested clears they risk losing other unknown potentially desired traits that are carried in the same area of DNA.
- The best science suggests that if animals have merits that are needed then they should not be removed from a breeding programme for a "problem" that has a DNA test. By going the short or quick fix route of clear to clear only matings; breeders are not using the tests inline with best scientific advice, and they may inadvertently be damaging the breed by removing not just the undesired genes but also some other closely linked genes too.