Understanding COI and ALC

Coefficient of Inbreeding (COI)

COI estimates the probability that two copies of a gene in an offspring are identical because they came from the same documented ancestor. A higher COI indicates more repeated ancestry within the pedigree. A lower COI indicates less documented relatedness, but it does not guarantee health or genetic diversity outside the recorded pedigree.

Ancestor Loss Coefficient (ALC)

ALC describes how many unique ancestors are present compared with how many ancestor positions exist in the generations being examined. Repeated ancestors reduce ALC because one individual occupies more than one position in the pedigree. ALC helps show pedigree repetition from a different perspective than COI.

Why both numbers matter

COI focuses on inherited relatedness, while ALC focuses on repeated ancestors and loss of unique ancestry. Reviewing them together can make pedigree concentration easier to recognize. Neither calculation should be used as the only breeding criterion.

Pedigree completeness matters

Calculations are only as complete as the recorded ancestry. Unknown parents and missing generations can make a result appear lower or less concentrated than the full biological pedigree. PSG Database therefore displays known positions, unique ancestors, and completeness alongside COI and ALC.

Using the calculations responsibly

Use COI and ALC with health history, temperament, age, veterinary information, lineage concerns, genetic evidence, and responsible breeding goals. They support informed planning, but they do not certify that a pairing is healthy or appropriate.