D. melanogaster sample locations, schematic gene structure of Hsp83 , and the P element insertion site. (A) Distribution of the natural fly populations collected around the world. Dots indicate the collection sites. The three red dots indicate the samples where a P element insertion into Hsp83 was found. The finnish population (F15 in additional file 1) is not shown. (B) Intron-exon organization of Hsp83 and the insertion of a P element into the proximal promoter of Hsp83. Below the Hsp83 gene structure an enlargement of the organization of cis-regulatory elements HSC1, HSC2 and HSC3 in the Hsp83 promoter region is shown. The 8-bp sequence (CTCTAGAA) flanking the P element is a direct repeat of the heat shock consensus elements created by the P-element insertion. The arrow above the P element shows the element's orientation. HSC, heat-shock consensus element (Xiao and Lis 1989). The structure is not drawn to scale.