Chromosomal polymorphism in Drosophila subobscura at different elevations in central Chile.

Samples of D. subobscura were collected at four localities, one at sea level and the three others at 620 m, 1,016 m and 1900 m elevation in the pre-andean zone of Central Chile, where the species is very abundant since its first detection in 1978. Cytogenetic analysis were performed on F1 larvae resulting from laboratory crosses of wild males and homozygous virgin females for all the chromosomal arrangements. The observed frequencies of homozygotes and heterozygotes for 19 different gene arrangements present in the populations, fit very well with the expected frequencies estimated according to the Hardy-Weinberg equilibrium. In comparing the gene arrangement frequencies, interpopulational differences were observed, suggesting an incipient process of microdifferentiation, that does not follow a clinal variation according to the altitudinal gradient.