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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