DESCRIPTION (provided by applicant): The long-term goal of this work is to use the model organism, Drosophila melanogaster, to investigate the genetic control of genomic imprinting. Genomic imprinting has been shown to be a general property of the Drosophila Y chromosome. Typically, a paternal imprint leads to repression of Y-linked reporter genes, while a maternal imprint gives relatively high expression of those genes. DNA methylation, histone methylation, histone acetylation, and chromatin structure are all candidates for generating a parent-specific imprint. We will investigate candidate genes that are known to be involved in these processes for their role in generating an imprint. We will also undertake a genome wide screen for genes that play a role in imprinting with a screen for quantitative or qualitative modifiers of the imprint. We will investigate reporter transgenes located in X chromosome heterochromatin for response to an imprint to determine whether imprinting is a Y chromosome phenomenon or a sex chromosome phenomenon. Finally, we will carry out sets of experiments aimed at elucidating the biological rationale for imprinting in Drosophila. Specifically, three hypotheses will be tested: that paternal imprinting is needed for proper expression of the Y fertility factors; that imprinting is a mechanism for silencing the transposon load carried by the Y chromosome; and, that imprinting is a mechanism for controlling expression of the rDNA. The results of these experiments will have implications for understanding human genetic disorders arising out of imprinting, and for the evolution of imprinting in general.