INTERCHROMOSOMAL EXCHANGE OF GENETIC INFORMATION BETWEEN GENE ARRANGEMENTS ON THE 3RD CHROMOSOME OF DROSOPHILA-PSEUDOOBSCURA

During the last 60 years, the inversion polymorphism on the third chro mosome of Drosophila pseudoobscura has become a case study of the evol ution of linked blocks of genes, isolated from each other by the suppr ession of recombination in heterozygotes for different inversions. Due to its location within inverted regions in most gene arrangements, th e amylase (Amy) gene region can be used to elucidate the molecular pat tern of evolution in these inversions. We studied this region in the T ree Line phylad of gene arrangements, with regard to both restriction site polymorphisms (RSP) and nucleotide sequences. The analysis of res triction maps, encompassing 26 kb, corroborates the cytogenetic phylog eny established on the basis of inversion breakpoints. However, we fou nd that the 2.7 kb of nucleotide sequences of the Amy1 gene are identi cal in both Estes Park and Hidalgo arrangements, despite the fact that these inversions arose independently from Tree Line. These contrastin g results suggest that a homogenizing force, most likely gene conversi on, is able to bring about localized exchanges between otherwise isola ted gene arrangements.