Founder effect

In population genetics, the founder effect is the loss of genetic variation that may occurs when a new population is established by a very small number of individuals (e.g. a single pregnant female, a single pair, or a small number of conspecifics ) from a larger population. The founder effect is the phenomenon whereby new colonies of a given species may become instantly distinct from the original population as a result of being founded by a portion of small atypical members of the parent population. The founder effect is a special case of genetic drift and is a stochastic or random genetic process.

Size restrictions through which populations may pass are called bottlenecks. A particular case occurs when a population is established by a small number of colonists or founders. Genetic drift that follows is often called the founder effect. Ernst Mayr defined the founder effect as:

the establishment of a new population by a few original founders (in a extreme case, by a single fertilized female) which carry only a small fraction of the total genetic variation of the parental population

The Mayr's theory in which speciation by founding principle is the context where most of the evolution could, according to him, hypothetically occur is the theoretical foundation of the idea of punctuated equilibrium.