The segregation distortion (SD) phenomenon in wild populations of Drosophila melanogaster: interaction between chromosomes 3 and SD chromosomes 2.

The Segregation Distortion (SD) phenomenon is a typical case of non-Mendelian segregation in Drosophila melanogaster, due to the dysfunction of sperm bearing a non-SD homologous chromosome. In nature, several factors involved in the expression of the SD phenomenon have been described; among these, a genetic modifier carried by chromosome 3, which enhances the distortion effect of the SD chromosomes. The analysis of natural Sardinian populations, carried out in order to evaluate the presence of chromosome 3 bearing these enhancer factors, has enabled us to ascertain that (a) also in these populations chromosomes 3 with enhancer factors are present, although with frequencies lower than those previously reported in other publications; (b) among these enhancer chromosomes 3, some increase the k of certain chromosomes 2 from values of chromosomes considered non-distorting (k less than or equal to 0.66) to value typical of SD chromosomes. The data obtained also allow us to put forward some considerations regarding the dynamics of the SD phenomenon in Sardinian populations, where the frequency of SD chromosomes is fairly elevated.