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Two male sibs believed to be examples of meiotic recombinants between the closely linked loci for G6PD deficiency of Mediterranean type and severe deutan color blindness proved to be simple segregants of a triplo-X mother of genotype d--GdMediterranean/d+GdMediterranean/d+GdB. This finding suggests that in Sardinia the linkage between the two loci under consideration may be tighter than previously assumed.

The authors report data on the genetic distribution of thalassaemia and of glucose-6-phosphate dehydrogenase deficiency in the populations of certain Sardinian villages, many of which are not only of great antiquity but have maintained isolation for very long periods and therefore possess the following three requirements for suitability for investigation of the possible interrelationships among malaria, thalassaemia and G-6-PD deficiency: a reasonable degree of ethnic homogeneity, availability of reliable demographic data, and availability of malaria-free populations of adequate size and of ethnic background and genetic isolation similar to those of the malarial populations.Investigations including more than 6000 observations in 52 villages demonstrated a positive correlation between the incidences of thalassaemia and G-6-PD deficiency. It is suggested that the genotype that carries thalassaemia and/or the enzyme deficiency may have a high adaptive value in a malarial environment.It is concluded that there is a need further to investigate human genetic structure and the biological fitness of the principal genotype combinations in both existing environments and those that will result from continued cultural evolution.