Maintaining the integrity of genomic DNA is crucial to cellular function and survival. Proteins such as Bloom (BLM) DNA helicase function to protect the genome from the deleterious effects of both exogenous and endogenous sources of DNA damage. Loss of BLM activity in humans leads to the rare autosomal recessive disorder Bloom Syndrome, which is characterized by developmental abnormalities, premature aging, and cancer susceptibility. The goal of this proposed research is to investigate the role that BLM plays in preventing DNA damage associated with repetitive DNA sequences. Due to the functional conservation between human BLM and Drosophila melanogaster Blm proteins, we propose to use Drosophila as a model for studying the Blm-dependent replication challenges posed by repetitive DNA sequences. The cellular consequences of repeat-dependent replication challenges to Blm remain unknown, but the Drosophila embryo provides us with a useful model for studying these aspects of Blm function. Our previous data suggest that Blm facilitates replication of repetitive DNA sequences, particularly the highly repetitive Y chromosome, during early embryo development. We propose to identify the repetitive sequences on the Y chromosome that pose Blm-dependent replication challenges and to investigate long-term effects of Blm-deficiency during early development. We will address these questions in Aim 1 by exploiting natural variation in Y-linked repetitive DNA sequences in Drosophila to define specific Blm-dependent sequence motifs on Y chromosomes. To accomplish this, we will screen for lines displaying Y-linked, Blm-dependent variation and then analyze whole genome sequences of these lines for differences in Y chromosome repetitive DNA content. Long-term biological effects of Blm-deficiency during embryogenesis will be investigated in Aim 2 by comparing Blm heterozygous flies that developed with or without maternal Blm for a variety of phenotypes that might be affected by sub-lethal amounts of DNA damage. Those phenotypes will include lifespan, fertility, body composition, and locomotor activity. Lastly, in alignment with the goals of the SuRE program, Aim 3 of this grant will provide high-impact intensive undergraduate research training of undergraduate students who are underrepresented in biomedical research. This proposal will provide students with direct participation in the execution, analysis, and reporting of this research and will support the growing reputation of LC State as a vibrant institution for future biomedical scientists and healthcare professionals that come from diverse backgrounds.