There are two copies of each gene, one from the mother, one from the father. That is the only actual hard and fast rule in genetics, since there could actually be 0 - 100% of the genes from each of the grandparents or beyond. On average, however, each grandparent would be assumed to contribute 25% of the genes. The Coefficient of Inbreeding, or COI, indicates the likelihood that both copies of any one of a dog's genes come from the same ancestor. The higher the value, the more times ancestors appear in both sides of the pedigree. Line breeding is done to help fix characteristics of breed type. Excessive line breeding, which would have a high COI, leads to inbreeding depression which is associated with a loss of genetic diversity: decreased lifespan, fertility issues, reduced litter sizes and birth weight, increased incidence of cancer and autoimmune diseases.

Berner-Garde has implemented calculation of the COI with a base year of 1966. What this means is that the calculation of COI for a dog uses all ancestors of that dog who were born in 1966 or later. This results in the COI calculations for all dogs going back to the same group of ancestors, providing a better estimate of the COI for use in comparing different possible breedings than using a fixed number of generations. However, this method requires us to know the whelp date for each dog as that is what determines whether to include that dog or not.

Percent Blood is an estimate of the percentage of possible contribution of genes from any given ancestor.

To make our averages more meaningful when considering new matings, the table below shows the average COI calculated for litters born in 2008 or later, calculated using the BG Base Year method. The average is shown for each number of complete generations along with the number of litters used to calculate those averages. Breeding for a COI of less than the breed average would be ideal. But as with any breeding selection, COI is just one aspect of the whole dog that can be taken into consideration. This also makes three numbers important, the COI, the total number of dogs in the evaluated pedigree, and the number of complete generations.