- DB setup
- Key Dogs
No Wiston Cap
Cap and Cap
Number of dogs
#Pups per dog
Where do they go
17 Mar 2012
Teun v/d Dool
STATISTICS FROM THE STUD BOOKSCopyright © Teun C. van den Dool, Jan 2002
press here for a Dutch revision
4. INBREEDINGA small (effective) number of ancestors combined with line breeding or inbreeding can result in a highly inbred gene pool. A figure commonly used to indicate the amount of inbreeding is the Coefficient of Inbreeding (CI). CI is equal to the relationship or Kinship coefficient of its parents. CI is the probability that two genes chosen at random from distinct individuals are identical. An individual with equal genes is called homozygous (for this part of its chromosomes).
The following formula, commonly attributed to Sewel Wright (1922), is used to calculate the CI of dog X in a simple way:
As an example take the (partial) pedigree depicted in figure 5. There are 6 paths via 3 common ancestors (31154, 82022 and 88472) of which the CI's are indicated. The formula is applied as follows:
Summing gives a total CI=66.7%. Five Dogs have such a high CI. It actually is 66.9% due to some more common ancestors further back in time. These dogs were an attempt of Edward Smith to breed back to Wiston Cap 31154. None of these five dogs produced sustained progeny. David Rees and Roy Goutte wrote articles on these Dogs in WSN (see the references). These dogs had 87.7% of Wiston Cap's blood in the definition of figure 2. Even if these figures would be 100% it would not guarantee a copy of Wiston Cap as it would give a random mixture of its chromosomes. Often such breeding will result in illnesses, as it did in this case, although apparently it also produced excellent Wiston Cap-like copies.
Figure 6 shows the resulting CI's as a function of the year in which the pups were born. Some CI's higher than 40% stand out:
Before 1950 a line can be seen at CI=25% (and less clear at 12.5% and 6.25%). A CI=25% is obtained by matings between parents and children or between siblings. After 1960 this line becomes vague and increasing due to influence of older generations in the pedigrees. This is also the reason why in recent years hardly any dog can be found with a CI lower than 4%. And even then most of them come from ROM (Registered On Merit) dogs.
Normally, people would look at pedigrees with 6 generations at most. Figure 7 shows the CI's when one would only use that information. This line shows a decreasing trend. The difference with a full pedigree is 7% maximum. So on a short term we may be more outcrossing than in the past, but in reality there is still an increased inbreeding. This is characteristic for closed populations with selective mating.
Over the last 10 year the CI was 7% on average. Is that high or low? I have the feeling that it is on the low side compared to many other breeds. More than 40% would be considered high by almost everybody, although not uncommon in many other breeds. Near 0% in 10 generations would be considered very low, and it is 4-5% on that time-scale. Probably the average CI is a little higher because the known founders were inbred themselves.
A CI of 7% is certainly low considering the small genetic diversity in the current population (effectively the genomes of 8 dogs). More inbreeding would: