Pedigree Completeness & COI
What is COI?
The Coefficient of Inbreeding (COI) measures how likely an animal is to inherit two copies of the same allele from a common ancestor. A higher COI means more inbreeding; a lower COI suggests greater genetic diversity.
COI is widely used by breeders to make pairing decisions — but it is only as accurate as the pedigree data behind it.
Why pedigree completeness matters
COI calculations work by tracing ancestral lines and finding common ancestors — animals that appear on both the sire's and dam's side of the pedigree. If ancestors are missing from the pedigree, common ancestors can't be detected, and the calculated COI will be artificially low.
This is the single biggest risk with COI:
- A reported COI of 3% does not mean the true inbreeding is 3% — it means the inbreeding is at least 3% based on the data available.
- Missing ancestors = missing inbreeding loops = understated COI.
- The more generations that are incomplete, the more the COI underestimates the true value.
Example
Consider two animals whose 4-generation pedigree shows only 6 out of 14 possible ancestors. The COI might calculate as 0% because no common ancestors are visible. But if the missing 8 ancestors were filled in, you might discover shared great-grandparents that push the real COI to 12% or higher.
How BreederPro helps
BreederPro shows a pedigree completeness indicator on the Pedigree tab. This tells you what percentage of ancestor slots are filled for the selected number of generations.
| Completeness | What it means |
|---|---|
| 80–100% | Strong foundation for genetic analysis. COI estimates are reasonably reliable. |
| 50–79% | Some gaps exist. COI is likely understated — treat it as a minimum estimate. |
| Below 50% | Significant data gaps. Any COI calculation would be misleading and should not be used for breeding decisions. |
What to do about incomplete pedigrees
Add external animals — If an ancestor isn't in your care, add them as an External animal. They won't appear in your main Animals list but will fill in the pedigree tree. See Pedigree & Lineage for details.
Use registry databases — Breed registries (e.g., TICA, CFA, AKC, UKC) maintain extensive pedigree databases. Cross-reference their records to fill in missing ancestors in BreederPro.
Aim for 5+ generations — COI becomes meaningful at 5 or more complete generations. Three generations is a bare minimum and will miss many inbreeding loops.
Build bottom-up — Start by adding the oldest known ancestors (great-great-grandparents), then work forward. This fills in the most ancestor slots with the least effort.
Key takeaway
A low COI does not mean low inbreeding if your pedigree is incomplete. Always check pedigree completeness before making breeding decisions based on COI values. When in doubt, consult your breed registry's database for complete lineage records.