Studying pedigrees sooner or later you will stumble upon the expression “COI”. Without getting too academic I will try to explain what the Coefficient of Inbreeding is.

COI (Coefficient of Inbreeding) COI or IC (Inbreeding Coefficient) is the probability of having two versions of the same gene because of common ancestors. These different versions of a gene are called alleles. Alleles can be either dominant or recessive. Every individual normally gets 50% of its genes from each parent. However two full siblings may not get the same subset of genes from a given parent so the heritage of full siblings can range from identical to as diverse as the heritage of the parents.

The COI increases with the number of generations calculated, each jump considers exponentially more ancestors. Please bear in mind that a COI value without the specification of used generations is not significant. The example below shows the COI of the same dog calculated with different numbers of generations:

COI: 1.03567%
Number of generations=8
Total number of unique ancestors=260
Total number of ancestors=506
Total number of possible ancestors=510
COI: 3.39425%
Number of generations=12
Total number of unique ancestors=971
Total number of ancestors=7711
Total number of possible ancestors=8190
COI: 10.5774%
Number of generations=18
Total number of unique ancestors=3473
Total number of ancestors=452965
Total number of possible ancestors=524286

Most online pedigree databases show the COI, some also offer the possibility to calculate it, also for “test-matings”. Those calculations are accurate to the point that they are based upon the information in the database. The more dogs (ancestors) are entered, the more accurate the result will be.

In a nutshell, the COI is a number that states the Inbreeding Percentage of a dog.
There are dissenting opinions about the allowable COI for a mating, however, some breed clubs make their approval of a mating dependent on a low COI.


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