Latitude-correlated genetic polymorphisms: selection or gene flow?

Latitude-correlated polymorphisms can be due to either selection-driven evolution or gene flow. To discriminate between them, we propose an approach that studies subpopulations springing from a single population that have lived for generations at different latitudes and have had a low genetic admixture. These requirements are fulfilled to a large extent by Ashkenazi and Sephardi Jews. The original population lived at a latitude of 35 degrees N, where the Sephardis still live. The Ashkenazis, however, moved to a latitude of 50 degrees N, starting about 10 centuries ago. The present study examines 3 latitude-correlated polymorphisms: PGP, PGM1, and AHSG. We found that PGP*2 and AHSG*2 alleles most likely underwent selection-driven evolution, but that PGM1*ts allele was not similarly affected. Since temperature might have been considered a reasonable selective factor, we also studied a population living at >800 m above sea level from Aosta Valley (Italy).

Population genetic studies on Jews. I. The alpha 2HS serum glycoprotein, a polymorphism strongly correlated with latitude.

A sample of Jews subdivided according to the birth-place of their parents or grand-parents have been examined for a large number of genetic markers in the course of a long-term project on the genetics of Jews. We report here the findings concerning 794 Jews studied for the AHSG polymorphism. All the subsamples were in Hardy-Weinberg equilibrium. A highly significant difference was found between Sephardic + Near East Jews and Ashkenazi (AHSG*2 frequencies: 0.184 +/- 0.015 and 0.258 +/- 0.016, respectively). For comparative purposes the data available on Caucasoids have been considered. It turned out that they were neatly arranged along a latitude-AHSG gene frequency cline (0.0092 of AHSG*2 gene frequency increase per degree of increase of latitude) in the explored 30 degrees-60 degrees range (r = 0.97; P much less than 0.001). Of the two Jewish frequencies that could be taken into consideration because of their sufficient sizes, that of the Near East + Sephardic Jews was perfectly in line with the above mentioned cline, while that of the Ashkenazi was somewhat displaced in the sense of being more similar than expected to the other, more southern, Jewish group. Since the only AHSG*2 frequency significantly displaced from the regression line is that of the Ashkenazi, whose ancestors lived until centuries ago in more southern areas, this finding is a strong confirmation of the observed cline.

Researches on the biology of Himalayan populations.

This long term project is aimed to study the following points: 1. Evolutionary adaptation to high altitude. 2. Population genetics of high altitude populations and 3. Mechanisms of resistance to malaria in some of these. The study suggests that the Sherpa of Nepal and the Quechua of Peru, living at altitude about 4000m, may have adapted to low oxygen pressure. The results of biochemical marker studies show that the Himalayan populations may remain genetically separated even when sharing the same village. Studies relating to resistance to falciparum malaria indicate that the immunity, conferred on the Tharu against malaria, may not involve erythrocytes exclusively.