The Drosophila Y chromosome is an unusual molecule. It represents nearly 20% of the D. melanogaster genome, but contains only 0.1% of the protein coding genes present in its genome. Instead of genes, the Y chromosome consists almost entirely of multimegabase long, highly repetitive, and transposon-rich constitutive heterochromatin. A simplistic view might suggest a lack of function to this multimegabase highly repetitive molecule. However, our studies indicate that geographically distinct Drosophila Y chromosomes affect classical phenotypes, such as position effect variegation, fertility, and male courtship and fitness. In addition, Drosophila Y chromosome can modulate expression from hundreds to thousands genes in XY males and XXY females genotypes carrying a Y chromosome copy. The Y-regulated genes are consistently associated with key chromatin components, immune response genes, and mitochondrial-related genes. The molecular mechanisms underlying this process are unclear. Hence, under supervision of Dr. Bernardo Lemos, I am investigating the mechanisms by which Y-linked heterochromatic repeats modify the euchromatic epigenome and relate these mechanisms to genomic responses to environmental exposures and human health.