A Coefficient of Inbreeding (COI) calculator measures the genetic relatedness of a potential mating pair. It tells you the probability that two copies of a gene — one from each parent — are inherited from a common ancestor. For Harlequin breeders, this is a critical tool for maintaining genetic diversity while building toward the AP (American Purebred) goal.How to Use It
A low COI doesn't guarantee a perfect match — but it gives you the data you need to make smarter decisions for the future of your flock and the Harlequin breed.
Inbreeding depression is a real risk in any rare breed population. High COI values can lead to reduced fertility, weaker immune systems, smaller lamb crops, and hidden genetic faults. Strategic mate selection — keeping COI below 10% and ideally under 5% — keeps your flock healthy, productive, and resilient.
Enter the registration numbers or names of the ram and ewe you're considering pairing.
Select the generation depth (we recommend 5-10 generations for accuracy).
Click Calculate — the tool scans shared ancestors across both pedigrees.
Review your results: COI %— the coefficient of inbreeding for this pairing
Shared ancestor breakdown — which ancestors appear on both sides
Risk level— low (under 5%), moderate (5-10%), or high (over 10%)
Use the data
— A low COI means more genetic diversity and healthier lambs. High COI doesn't mean you can't breed them, but it's a signal to proceed with caution and plan for.
Aim for COI under 5% for breeding stock, and keep it under 10% for any pairing. The lower the number, the better for long-term flock health.