Inbreeding analysis
Coefficient of inbreeding, counted loop by loop.
The coefficient of inbreeding (COI) is the probability that an animal inherits two copies of the same gene from one ancestor. It depends on how many generations of pedigree you count, so only compare COIs worked over the same depth. Choose a pairing below and every loop behind the number is drawn and summed.
What's a good COI? There is no single threshold. Clubs set bands for their own breed, because a figure that is normal in one closed studbook is high in another. As a reference point, first cousins give 6.25%, half siblings 12.5% and full siblings 25%.
Instrument No. 001 · Inbreeding analysis · Example animals
Choose a pairing. Every loop through a shared ancestor is counted.
Coefficient of inbreeding · Example data
Coefficient of inbreeding 12.5%
F = Σ (1/2)n1+n2+1 (1 + FA)F = (1/2)^3(1 + 0) = 0.125
Loop 1: Offspring of this pairing, Ridgeview Juniper, Ridgeview Atlas, then back down through Ridgeview Atlas, Aldergrove Tess.
Your registrar can run this on your own studbook
In Breed Ledger, a pairing calculates the COI from up to eleven generations of your registry's records and shows it, the repeated ancestors and how complete the pedigree is.
Read the loops, not the total
Two pairings with the same COI can carry it through one close ancestor or several distant ones. The loops tell you which.
Keyboard and screen readers
Every control is a select or a button. The result and the selected loop are announced as they change.
Loops, not ancestors
COI counts paths, not names
A shared ancestor adds one term for every separate route from the sire up to it and back down to the dam. When an ancestor appears on both sides only because its offspring does, it adds nothing of its own: the closer ancestor already carries it. That is why the half-sibling pedigree shows its grandparents hatched.
Distance halves the effect
Each generation halves the term
A grandparent shared by the sire and the dam adds (1/2)^5, or 3.125%. A great-grandparent shared by both adds (1/2)^7, or 0.78%. Close loops carry the largest terms, which is why a three-generation pedigree catches the biggest ones and a deeper studbook finds the rest.
Instrument No. 001b · Pedigree COI and genomic COI · Example data
One pedigree value, six DNA results.
A pedigree COI is an expectation: the share of the genome two parents are expected to pass on from the same ancestor. A DNA test measures what one animal actually inherited. Full siblings with the same pedigree COI test differently, and so do labs.
- Test A · sibling, 9,000 markers9.9%
- Test B · sibling, 220,000 markers11.8%
- Test C · same animal as B, lab 215.7%
- Test D · sibling, 650,000 markers14.3%
- Test E · sibling, segments over 4 Mb only15.5%
- Test F · sibling, 220,000 markers18.4%
Mendelian sampling
Each parent passes a random half. Some offspring inherit more of a shared ancestor than the pedigree expects, some less.
What the test counts
Marker density and the shortest run of matching DNA a lab counts change the result. Short runs reach further back than any pedigree.
How deep the pedigree goes
A three-generation pedigree misses older shared ancestors that DNA still sees, so genomic values can sit well above it.
Questions
Questions about COI.
What is a good COI?
How is COI calculated?
Why do two COI calculators give different numbers?
Download the COI policy template (PDF, 60 KB)Download the one-page version (PDF, 42 KB)
Book a demo
Run this on your own studbook.
Book a demo and I will run pairings from your own records with your registrar.