What is COI (Coefficient of Inbreeding)?

The coefficient of inbreeding (COI) is a measure of genetic similarity that quantifies the probability that two alleles (gene variants) at a given genetic locus in an individual are identical by descent (IBD). This metric helps assess the level of inbreeding in an individual, where a higher COI indicates a higher likelihood that the individual inherited the same allele from both parents due to shared ancestry.

What Do Different COI Values Mean?

A COI ranges from 0 to 1 (or 0% to 100% in percentage terms). A COI of 0 means the individual has no inbreeding, while a COI of 1 (100%) means the individual is completely inbred (both alleles at every genetic locus are IBD).

How is COI Calculated?

This is calculated by analyzing the individual's ancestry via its pedigree. It considers the probability that both parents share common ancestors and that these ancestors contributed identical alleles.

The basic formula involves summing contributions from all shared ancestors:

where 𝑛 1 and 𝑛 2 are the number of generations from the individual to the shared ancestor through each parent.

Example COIs

A COI of 0.125 (12.5%) corresponds to a mating between first cousins.
A COI of 0.25 (25%) corresponds to a mating between siblings or a parent-offspring pair.

How Does This Site Calculate COI?

Due to the recursive nature of the algorithm, the calculation of a COI is rather resource intensive, and takes several seconds to calculate for each individual dog, so it is not advisable to compute it on-demand on this website. While we have made attempts to optimize the calculation process, it is necessary to perform database-wide calculations via a back-end proccess. As a result, the COIs displayed on this site are only updated periodically, and may not reflect immediate changes (such as the filling in of further generations of ancestry).