Pedigree Analysis of Individual Bull Terrier Dogs

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 Medicine

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 dam’s 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 doesn’t 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 doesn’t appear until the 12th generation, but appears 57,758 times, and Regent Pluto, who doesn’t appear until the 16th generation, but appears 697,250 times, and is more influential than any single great-grandparent.

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 dam’s 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 doesn’t appear until the 11th generation, but appears 10,454 times, providing almost 1/3 of the genes in the pedigree. Regent Pluto again doesn’t 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 doesn’t 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%.

04062006 Reprint for www.btca.com