Genetic Diversity / COI Calculator
The Coefficient of Inbreeding (COI) is the single most important number in ethical breeding decisions. It measures how genetically similar the sire and dam are — the higher the number, the greater the risk that hidden recessive diseases will express in the litter. This calculator gives a quick estimate based on shared ancestors and generations back, plus context on what each COI band means (0-6.25% ideal, 25%+ full-sibling level and dangerous). For final decisions, always run a full 10-generation pedigree COI through breed-club or veterinary software.
Full 5-generation pedigrees give the most reliable estimate.
Reference bands:
- 0-6.25% — unrelated to distant cousins (ideal)
- 6.25-12.5% — first-cousin equivalent
- 12.5-25% — half-sibling equivalent
- 25%+ — full-sibling / parent-offspring (avoid)
For accurate pedigree-based COI, use software like Breedmate or the breed database's COI calculator with a full 10-generation pedigree.
How it works
Canine Population Genetics, Wright's Inbreeding Coefficient (COI), and Pedigree Health
Canine population genetics analyzes the distribution of genetic variation within domestic breeds. Modern purebred dogs operate within closed studbooks that are vulnerable to inbreeding depression, loss of Major Histocompatibility Complex (MHC) immune diversity, and the amplification of deleterious recessive mutations.
The gold standard metric in population genetics is Sewall Wright's Coefficient of Inbreeding (COI), endorsed by the Orthopedic Foundation for Animals (OFA) and the Institute of Canine Biology.
Wright's Coefficient of Inbreeding (COI) Scale: - COI < 5.0%: Low Inbreeding (Excellent genetic diversity; reduced risk of complex recessive genetic diseases) - COI 5.0% to 10.0%: Moderate Inbreeding (Acceptable working threshold in preservation breeding) - COI > 12.5%: High Inbreeding (Equivalent to mating half-siblings; significant inbreeding depression) - COI > 25.0%: Extreme Inbreeding (Equivalent to mating full brother and sister or parent to offspring) Biological Impact: Every 10% increase in COI reduces median canine lifespan by 1.0 to 1.5 years and decreases litter size
The Popular Sire Effect & Genetic Bottlenecks
The single greatest driver of inherited canine genetic disease is the Popular Sire Effect:
- When a single champion show male is bred to hundreds of females, his unique deleterious recessive mutations proliferate through the entire global breed gene pool.
- Decades later, mating seemingly unrelated dogs results in severe genetic diseases (like dilated cardiomyopathy in Dobermans or syringomyelia in Cavaliers).
Evaluate stud breeding terms with Stud Fee Calculator, track pregnancy curves via Dog Pregnancy Calculator, estimate litter sizes with Litter Size Predictor, and explore population genetics at the Institute of Canine Biology.
Examples
- 1 shared ancestor 5 generations backCOI ≈ 0.05% (Low)
- 3 shared ancestors 3 generations backCOI ≈ 2.3% (Low)
- Full-sibling pairingCOI ≈ 25% (Very High — do not breed)