42 Saber Tails Winter 2016
Petit Basset Griffon Vendéen Club of America
inbreeding for that breed. The more frequent the muta-
tion is the more slowly it should be eliminated. Calculat-
ing the true frequency of a mutation is not trivial, and re-
quires a random subset of a breed be screened. Dogs that
are tested once a commercial DNA test becomes available
are not always representative of the breed as a whole, and
similarly cohorts of dogs that have been sampled by a re-
search institute during development of the DNA test are
also rarely characteristic of the breed.
The frequency of a mutation is typically expressed as the
fraction of chromosomes in a population that carry the
mutation. For example, if the frequency of a mutation
is described as 0.1, this means that 10% of the chromo-
somes in that breed carry the mutation and the remain-
ing 90% carry the normal copy of DNA. If 10% of the chro-
mosomes carry the mutation then just under 20% of dogs
are expected to be carriers and about 1% of dogs will be
affected.
Breeding Advice
Carriers should always be included in the first one to two
generations that follow the launch of a DNA test for a re-
cessive mutation, regardless of the frequency of the mu-
tation, to give breeders the opportunity to capture desir-
able traits, such as breed type and temperament, before
they start to select for dogs that are clear of the mutation.
Specific breeding policy for future generations should be
breed-dependent and ideally formulated after consider-
ation of factors such as the population structure and rate
of inbreeding. But in general terms, carriers should only
be removed from the breeding population if the frequen-
cy of the mutation is below 0.01 (1%), as this will mean
only around 2% of dogs will be prevented from breeding.
Avoiding carriers of a mutation that is more frequent will
result in a greater number of dogs being prevented from
breeding and could lead to a detrimental loss of diversity
for the breed.
Cathryn Mellersh, Animal Health Trust, November 2011
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