The heat shock genes in the Drosophila montium subgroup: chromosomal localization and evolutionary implications.

The hsp70, hsp83, hsromega, and the small heat shock protein genes were mapped on the polytene chromosomes of six species, representative of the geographical distribution of the Drosophila montium subgroup of the melanogaster species group. In addition, based on hybridization conditions, the putative locus of the hsp68 gene is given. In contrast to the situation in the melanogaster subgroup species, the hsp70 locus is single in the montium species. The hsp83, hsromega and the small hsp loci are also single in the montium genomes studied here, a common feature of all Drosophila species. Among the hsp genes studied, the small hsp genes and the hsromega-homologous sequences exhibit a higher degree of divergence between the melanogaster and the montium subgroups. Our results support the idea that the montium subgroup species has a genome organization closer to that of the common ancestor compared with the melanogaster subgroup species.