Practical Genetics for Bull Terrier Breeders and Owners
Health Seminar presented to the Bull Terrier Club of
America, October 10, 2002
Jerold S Bell, DVM, Tufts University School of Veterinary
Emred Top Gun of Brobar has a 10 generation inbreeding
coefficient of 32.57%. He is more tightly bred than the average Bull Terrier.
Studying his pedigree shows that his sire and dam are half-sibs, sharing their
dam; Troublesome Angel of Brobar. Further, Brobar Troubleshooter is also a
triple great-grandfather. Just based on the half-brother x half-sister
relationship, this provides an inbreeding coefficient of 12.5%. The additional
20% of the inbreeding coefficient represents contribution of the other dogs that
appear in both the sire and damís side of the pedigree.
The relationship coefficient, which can also be approximated
by what is called the percent blood coefficient, represents the probable genetic
likeness between the dog whose pedigree is being studied, and a particular
ancestor. It is a measurement of the average percentage of genes the individual
and the ancestor should have in common.
The following is a pedigree analysis of Emred Top Gun of
Brobar. The common granddam, Troublesome Angel of Brobar has a 50 percent blood
coefficient: 25% as the paternal granddam, and 25% as the maternal granddam.
This should be compared to the expected contribution of the sire and dam, which
each contribute 50% of the genes, but only from one side of the pedigree.
Troublesome Angel provides genes from both sides of the pedigree, and therefore
is more influential than either the sire or dam. For a dog to be influential in
a pedigree, it has to appear behind more than one offspring. Otherwise, you are
only linebreeding on the single offspring, and only the 50% of genes that were
passed on by its parent.
Brobar Troubleshooter contributes 37.5% of the genes to the
pedigree. The next most influential linebred ancestor is Beechhouse Snow Vision,
who doesnít even appear until the 10th generation, but appears 3,337 times in
the pedigree, providing a percent blood coefficient of 29.36. Such founding
ancestors provide what is called the background inbreeding, and are what
established the pedigree base for the breed. If an influential ancestral dog
carried a detrimental recessive gene, it would be widespread in the breed. The
rest of the linebred ancestors in the pedigree are listed in the pedigree
analysis. Note Velhurst Vindicator, who doesnít appear until the 12th
generation, but appears 57,758 times, and Regent Pluto, who doesnít appear until
the 16th generation, but appears 697,250 times, and is more influential than any
Kilacabar Stand and Deliver has a 10 generation inbreeding
coefficient of 23.06%. He is mildly more inbred than the average Bull Terrier.
Joan La Pucelle is the paternal granddam, and the maternal great-granddam, with
a percent blood contribution of 37.5%. If you look at the pedigree of Kilacabar
Stand and Deliver, you see that Burundi Black appears as a double maternal
great-grandsire. However, his contribution is only from the damís side. While
she was linebred on Burundi Black, Kilacabar Stand and Deliver was not. From the
accompanying pedigree analysis, the rest of the inbreeding in this pedigree is
from background inbreeding. The second most influential ancestor is Beechhouse
Snow Vision, who doesnít appear until the 11th generation, but appears 10,454
times, providing almost 1/3 of the genes in the pedigree. Regent Pluto again
doesnít appear until the 16th generation, but appears 1,203,850 times, providing
12.57% of the genes to the pedigree.
Quicksilver Moustache Pete is an outbred dog, with an
inbreeding coefficient of 15.76%. His only ancestors common to both the sire and
dam are in the background, starting in the 9th generation. Beechhouse Snow
Vision first appears in the 10th generation, appearing 6,317 times, and
contributing 27.79% of the genes to the pedigree. Regent Pluto doesnít appear
until the 17th generation, but appears 950,690 times, contributing 12.06% of the
genes to the pedigree.
When doing pedigree analyses, it is important to study deep
pedigrees. At 5 generations, Emred Top Gun of Brobar has an inbreeding
coefficient of 18.63%. At 10 generations, it is 32.57%. At 5 generations,
Kilacabar Stand and Deliver has an inbreeding coefficient of 9.33%, compared to
23.06% at 10 generations. At 5 generations, Quicksilver Moustache Pete has an
inbreeding coefficient of 0%, while at 10 generations, it is 15.76%.