The founder effect is reduced and shifted genetic diversity in a population started by a small number of individuals. The founders carry only part of the source population's alleles, and by chance some rare alleles become common in the new population while others disappear.
In practice
Many cannabis seed lines began as founder events. A traveller brought back seed from a few plants of a landrace; a breeder started a line from one exceptional female and one male; a heirloom was passed on as a single packet. Each of these new populations reflects its few founders, not the full landrace.
That is why two "Afghan" lines from different collections can differ markedly, and why a line kept outside its source region may drift away from the original type. Records of how many plants founded a line, and from where, help breeders judge how representative it is.
Don't confuse with
- Genetic bottleneck: a crash in numbers within an existing population; the founder effect is the start of a new one.
- Selection: founders chosen for traits are both a selection and a founder event.
- Landrace: the source population, typically far more diverse than lines founded from it.
