What is it, what is not?
In population genetics, the founder effect is a loss in genetic diversity that occurs when a new population is established with a very small proportion of individuals from a larger population. It was first summarized in all its aspects by Ernst Mayr in 1952.
As the effect of a loss in genetic diversity, the new population may be distinctively different from the ancestral population, both genetically and phenotype. In extreme cases, the founder effect is thought to cause speciation and the subsequent evolution of new species.
As the picture shows, the original population had almost equal numbers of blue and red individuals. three smaller founder populations show a dominant (founder effect) color.