How to Calculate Coefficient of Inbreeding (COI) - Chapter for Dog Breeders

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The coefficient of inbreeding (COI) for breeding dogs can be calculated by examining the pedigree of the individual dog and identifying all common ancestors. The following steps can be used to calculate the COI:

1) Identify the common ancestors: Start by identifying all of the common ancestors in the pedigree of the individual dog. This includes any dogs that appear on both the sire and dam's side of the pedigree.

2) Determine the degree of relationship: For each common ancestor, determine the degree of relationship to the individual dog. The degree of relationship is expressed as a fraction and represents the proportion of genes that the individual dog inherited from that ancestor.

3) Calculate the probability of inheritance: For each generation between the individual dog and the common ancestor, calculate the probability of inheriting the same allele from that ancestor.

4) Multiply the probabilities: Multiply the probabilities of inheritance for each generation to obtain the COI for the individual dog.

Let us understand the above 4 points with an example. 

Let's say you want to calculate the COI for a dog that has a common ancestor 4 generations back on both the sire and dam's sides of the pedigree.

1) Identify the common ancestor: In this case, the common ancestor is the same dog on both sides of the pedigree, so it should only be counted once.

2) Determine the degree of relationship: The common ancestor is three generations back, so the degree of relationship is 1/16 or 6.25% for each parent.

Here's how I have arrived to 6.25% Relationship Degree

When a common ancestor is 3 generations back, the degree of relationship is calculated as 2^n (2 to the power n, where 2 is base and n is exponent), where n is the number of generations back to the common ancestor. In this case, the common ancestor is 3 generations back, so the degree of relationship is 2^4 (means 2x2x2x2), which is equal to 16. This means that the individual dog shares 1/8 or 12.5% of its genes with the common ancestor. So, in general, the degree of relationship is calculated by taking the number of common ancestors and the number of generations back to each ancestor into account. The closer the common ancestor is to the individual dog, the higher the degree of relationship and the higher the COI.

3) Calculate the probability of inheritance: For each generation between the dog and the common ancestor, calculate the probability of inheriting the same allele from that ancestor. For example, if the dog is the great-great-grandchild (4 generation) of the common ancestor, the probability of inheriting the same allele from that ancestor is 1/16 or 6.25% (for which the decimal value is 0.0625).

4) Multiply the probabilities: Multiply the probabilities of inheritance for each generation to obtain the COI. In this example, the COI for the dog would be (0.0625 x 0.0625) = 0.00390625 or 0.390625% (means 0.00390625 x 100%).


Hence the COI for a dog that has a common ancestor 4 generations back on both the sire and dam's sides of the pedigree will be 0.390625%.

Repeat this process for each common ancestor in the dog's pedigree to calculate the overall COI.

Related Links (Must Read the Below Links):

1. A Deeper Insight Into Coefficient Of Inbreeding (COI)


2. Is Low Coefficient of Inbreeding (COI) Always Good in Breeding Dogs?

Understanding the coefficient of inbreeding (COI) is important in dog breeding for several reasons:

Health concerns: Inbreeding can increase the risk of inherited health problems in dogs, and a high COI indicates a higher degree of relatedness and a greater risk of genetic health problems. By understanding the COI, breeders can make informed decisions to reduce the risk of inherited health issues in their breeding programs.

Genetic diversity: A low COI indicates a higher degree of genetic diversity, which is important for maintaining the health and vigor of a breed. Inbreeding can reduce genetic diversity, which can lead to a loss of genetic variability and an increased risk of inherited health problems.

Breeding goals: Understanding the COI is essential for achieving breeding goals. If a breeder aims to improve a certain trait, such as conformation or temperament, they need to carefully select breeding partners with low COIs to avoid the risk of genetic health issues.

Breeding Ethics: Responsible dog breeding is about producing healthy, well-tempered dogs that meet the breed standard. Understanding the COI is an essential part of responsible dog breeding because it allows breeders to make informed decisions that prioritize the health and well-being of the dogs they breed.

In summary, understanding the coefficient of inbreeding is an essential part of responsible dog breeding. By carefully selecting breeding partners to maintain genetic diversity, minimize the risk of inherited health issues, and achieve breeding goals, breeders can produce healthy, high-quality dogs that meet the breed standard.