An exciting recent finding of genetics has been the discovery that the genomes of organisms from bacteria to humans contain families of DNA sequences that have the ability to make new copies of themselves that can insert elsewhere in the genome. These are known as transposable elements (TEs). The insertion of a TE into or near a gene may cause a mutation with a harmful effect on the survival ability or fertility of the individual. For example, in humans TE insertions have been implicated in mutations causing hemophilia and breast cancer. The discovery of TEs has led to a debate on the nature of the forces that control the distribution of TEs within populations of their host species. Previous studies in Drosophila, yeast and bacteria have shown that, although several copies of members of the same family of TE may be present within a host individual's genome, different individuals may have different numbers of copies. Furthermore, these are generally found to be inserted into different places in different host individuals, suggesting that some force of forces are preventing TE's from filling up all the sites available for occupation within the genome. The present study is designed to help identify the nature of these forces Further data on the distribution of TE's within a population of Drosophila will be collected and compared with the predictions of theoretical models. This will provide a check of the generality of the observations mentioned above. In addition, tests will be made of the tendency of TEs to accumulate in regions of the genome where genetic recombination is restricted. Such a tendency is predicted by the hypothesis that genetic exchange between homologous TE's located in different locations can produce chromosomal damage that eliminates the TEs concerned, and hence acts to prevent their spread. One such region is known as the centric heterochromatin. This region has not previously been studied in detail because of technical difficulties associated with the abundance of highly repeated DNA sequences in this region. Recent advances in DNA technology mean that it is now possible to study TE abundance in the heterochromatin, and this forms a major focus of the project.
