An allele frequency change in an isolated part of a population, untypical of the original, is the:

1. Isolation of a small group can shift allele frequencies by chance. 2. An event may initiate an allele frequency change in an isolated part of the population. 3. If that change is not typical of the original population it is the founder effect. 4. The bottleneck effect instead wipes out much of an existing gene pool. _Source: OpenStax Biology 2e (CC BY 4.0), Ch 19 'The Evolution of Populations', sections 19.1-19.3_