Is a case of genetic drift in which rare alleles or combinations of alleles occur in higher frequencies in a population isolated from the general population?

Yes, this phenomenon is known as the "founder effect," a type of genetic drift. It occurs when a small group of individuals becomes isolated from a larger population, leading to a limited gene pool. Rare alleles or combinations of alleles can become more common in the new population due to the reduced genetic diversity and the random nature of allele frequency changes over generations. This can significantly impact the genetic structure of the isolated population.