A DUPLICATION INCLUDING THE Y-ALLELE OF LCP2 AND THE TRIM RETROTRANSPOSON AT THE LCP LOCUS ON THE DEGENERATING NEO-Y-CHROMOSOME OF DROSOPHILA-MIRANDA - MOLECULAR-STRUCTURE AND MECHANISMS BY WHICH IT MAY HAVE ARISEN

Evolutionary changes during the process of sex chromosome differentiat ion in Drosophila miranda are associated with massive DNA rearrangemen ts. Comparing the DNA structure of the larval cuticle protein (Lcp) re gion from the X2 and neo-Y chromosome pair, We observed insertions, de letions and a large duplication at the neo-Y chromosomal locus. The du plication encompasses a complete copy of the neo-Y allele of Lcp2, and the ISY3 and the ISY4 insertion sequences. The latter was identified as a retrotransposon, termed TRIM. ISY3 shows DNA sequence similarity to P element homologs identified in the Drosophila obscura species gro up. We were interested in mechanistic aspects generating the duplicati on. We cannot exclude unequivocally that unequal sister-chromatid exch ange could give rise to the observed duplication; however, recombinati on is a rare event in Drosophila males. Location and sequence of the r etrotransposon TRIM served as molecular markers allowing us to reconst ruct two intrachromosomal transposition events that could lead to the observed duplication.