Features such as migration waves, regional founder effects, several bottlenecks (caused by wars, famine, catastrophes of nature) and expansion periods in the global populations, along with sometimes dramatic isolation (caused by geographical, linguistic or cultural factors) of different populations, have molded the human gene pool and resulted in genetic differences between world populations. Also the prevalence of various diseases and disease mutations greatly varies within different populations, and a substantial amount of our understanding of the history of various population-specific differences has actually emerged from the studies of genetic diseases in different populations.