Effective Population Size

Effective population size (Ne) is a key population genetics metric measuring how many individuals in a breeding population actually contribute to the next generation's genetic diversity. In cannabis breeding, Ne differs from census population size because not all plants reproduce equally—some contribute disproportionately to offspring while others may be culled or sterilized. Breeders track Ne to understand genetic drift, inbreeding risk, and long-term stability in closed or small breeding lines. Understanding Ne helps predict whether a breeding program maintains sufficient genetic variation across generations or risks losing alleles through chance alone. This concept is especially relevant in stabilized strain development and heirloom preservation efforts.

Professional breeders calculate Ne to assess line viability before committing resources to multi-year projects. Low Ne signals elevated risk of inbreeding depression and loss of desirable trait expression, prompting decisions to outcross, expand parent stock, or source new genetics.