Question

What could be the possible result of founder effect on genetic variation?

Answer 1

A decrease in genetic diversity, an increase of detrimental genotypes appearing

Explanation:

In an area where the gene flow has been pinched and there is reduced amount of alleles you find only certain combinations of genes able to be made. Genetic diversity relies on things like mutation as well, but remember that on a secluded island where people's genes are only Gg, GG, gg, you're never going to get a Gh, or a GB.
This also means that if one of the sets of genes is detrimental, like if the recessive gg gene is fatal, since there's only G and g genes being thrown around, the likelihood that gg appears is much higher.