What Is Meant by Describing Modern Human Global Migration as a "Serial

What is meant by describing modern human global migration as a "serial founder effect"?

A) With each successive wave of migration into a new geographic area, each new population accumulated unique mutations, resulting in increased genetic diversity with distance from the population of origin.
B) With each successive wave of migration into a new geographic area, each new population represented a completely different set of unique alleles relative to the source population.
C) With each successive wave of migration into a new geographic area, each new population carried the same set of alleles, diverging from the source population only after accumulating unique mutations.
D) With each successive wave of migration into a new geographic area, each new population was a subset of the previous population, which resulted in reduced genetic diversity in the newly colonized region relative to the source region.