ashkenazi jews
Despite considerable uncertainty about the demographic history of Ashkenazi Jews and their ancestors, available genetic data are consistent with a founder effect resulting from a severe bottleneck in population size between a.d. 1100 and a.d. 1400 and an earlier bottleneck in a.d. 75, at the beginning of the Jewish Diaspora.
The relatively high frequency of alleles causing four different lysosomal storage disorders, including Tay-Sachs disease and Gaucher disease, can be accounted for if the disease-associated alleles are recessive in their effects on reproductive fitness.
References
Feder J, Ovadia O, Glaser B, Mishmar D. Ashkenazi Jewish mtDNA haplogroup distribution varies among distinct subpopulations: lessons of population substructure in a closed group. Eur J Hum Genet. 2007 Apr;15(4):498-500. PMID: 17245410
Slatkin M. A Population-Genetic Test of Founder Effects and Implications for Ashkenazi Jewish Diseases. Am J Hum Genet. 2004 Jun 18 PMID: 15208782
Colombo R. Age estimate of the N370S mutation causing Gaucher disease in Ashkenazi Jews and European populations: A reappraisal of haplotype data. Am J Hum Genet. 2000 Feb;66(2):692-7. PMID: 10677327