Human Populations Are Known to Isolate Themselves from Other Groups

Human populations are known to isolate themselves from other groups based on cultural identity,language religion,etc.Some of these communities in North America include the Ashkenazi (descendants of European Jewish communities,Yiddish speakers),the Cajun population of Louisiana,the Arcadian population of Canada,and the Old Order Amish community of Pennsylvania.One in every 27 members of the Ashkenazi community,the Cajun population of Louisiana,the Arcadian population of Canada,and the Old Order Amish community of Pennsylvania carry the recessive Tay Sachs gene (Tay Sachs disease is caused by a recessive mutation on chromosome 15,and children with Tay Sachs rarely live beyond age 5),but this recessive gene is only found in 1 of every 250 people in the general North American population.Explain the high incidence of Tay Sachs among the Ashkenazi,Cajun,Arcadian,and Old Order Amish populations.