Genetic and molecular characterization of chromosome three heterochromatin in drosophila melanogaster

Heterochromatin comprises approximately one third of the genome of the fruit fly, Drosophila melanogaster. It performs vital functions in chromosome segregation and cell division. One of the most interesting and unusual features of heterochromatin is its ability to silence genes artificially relocated near it, so the presence of active genes there is paradoxical. The presence of moderately and highly repeated sequences within heterochromatin and the absence of such features as meiotic recombination and polytene banding, make it difficult to study using standard genetic approaches. For example, although heterochromatin comprises approximately 60Mb of DNA, the earliest releases of the genome project included almost no heterochromatic sequence. More recent releases provide only about 21 Mb of sequence on a series of non-contiguous scaffolds, the majority of which remain unlocalized. My work has focused on two relatively poorly characterized heterochromatic regions: the right arm of chromosome 3 (3R) and a distal portion of 3L heterochromatin (distal h47). A large number of genetic mutations have been made via P-element insertion, excision and male recombination, and by X-ray mutagenesis. These mutations provide useful new tools for the identification and characterization of genes in these regions. In particular the deficiencies will allow a means for mapping computer generated gene models by PCR. The genetic and molecular tools developed for work with these previously unexplored regions will help advance our understanding of the organization and function of sequences in heterochromatin. They also provide a necessary foundation for a complete functional annotation of genes within these unusual and poorly understood regions of the chromosome.