Heterochromatin in developing systems: The role of the Y chromosome in sperm development in Drosophila melanogaster

The Y chromosome of Drosophila melanogaster has two types of loci. The first type of locus consists of single copy genes known as fertility factors. These are required only for sperm development. A P element mutagenesis screen was conducted to locate these factors. TEM reveals that P elements inserted into fertility factors give the same ultra structure phenotypes as deficiencies of the region. In addition, two new Y chromosome lines were isolated that have enhancer trap expression in testes. The second type of locus is repetitive. I conducted a screen of heterochromatic elements on the Y chromosome. This screen revealed repetitive loci that act as developmental modifiers. This was investigated using fusion proteins inserted in P elements. This study revealed that these repetitive loci are not unique to the Y chromosome and act in both the germline and soma as developmental buffers. The repetitive loci act to modulate the expression of genes. Manipulations of the Y chromosome to alter the amount of the repetitive loci present in a given fly suggest that when the balance of these repetitive loci is disturbed, developmental instability results. Investigations of loci on the Y, X and autosomes in different backgrounds suggests that there is substantially more variation in these elements in the X and autosomes than the Y. This is consistent with the selective sweep hypothesis of Drosophila Y chromosome evolution.