CRISPR-mediated mosaic analysis represents a transformative advancement in genetics research, offering unprecedented precision and versatility for studying gene function across diverse biological systems. This powerful approach enables researchers to generate genetically distinct cell populations within organisms, circumventing traditional limitations while providing novel insights into developmental biology, disease mechanisms, and cellular function. Understanding and improving CRISPR-based mosaic techniques are crucial for advancing our knowledge of genetic regulation and for developing more sophisticated tools for biomedical research and therapeutic interventions.In my dissertation research, I conducted a comprehensive investigation into enhancing the versatility, precision, and reliability of CRISPR-mediated mosaic analysis in Drosophila. The study focused on three main technological developments: establishing a genome-wide MAGIC toolkit for recombinase-independent mosaic analysis, exploring nickase-based alternatives to traditional CRISPR nucleases, and implementing anti-CRISPR proteins to control genome editing activity. In the first phase of my research, I established a complete genome-wide MAGIC (Mosaic Analysis by gRNA-Induced Crossing-over) toolkit that incorporates optimized designs for enhanced clone induction and more effective clone labeling in both positive and negative MAGIC systems. This comprehensive kit includes gRNA-markers for all chromosomal arms, enabling mosaic analysis of pericentromeric genes, deficiency chromosomes, and interspecific hybrid animals—applications that were previously impossible with traditional FRT/Flp systems. The optimized gRNA designs significantly improve clone frequency while enhanced marker systems provide better visualization across diverse tissue types. Next, I explored the potential of CRISPR nickases as safer alternatives to traditional Cas9 nucleases for mosaic analysis. I demonstrated that nickases can effectively induce crossing-over events while potentially reducing cytotoxicity and off-target effects. Through systematic analysis of nickase variants (D10A and H840A) and different nicking patterns, I identified key factors that influence clone generation efficiency. I also developed enhanced tools for generating tissue-specific nickases, including Gateway destination vectors and HACK donor systems for converting existing Gal4 lines. To further advance the field, my colleagues and I demonstrated that anti-CRISPR proteins, particularly AcrIIA4, provide robust and specific inhibition of Cas9 activity in both germline and somatic tissues in Drosophila. We developed AcrIIA4-bearing balancer chromosomes that enable stable co-maintenance of Cas9 and gRNA transgenes while preventing unwanted genome editing. These tools effectively address issues of leaky Cas9 expression that have historically limited experimental precision. We further characterized tissue-specific anti-CRISPR variants that provide spatial control over CRISPR activity and demonstrated the pronounced maternal effect of AcrIIA4, which extends inhibition beyond early embryogenesis. In summary, this dissertation describes advances in the versatility, precision and reliability of CRISPR-mediated mosaic analysis in Drosophila achieved through the development of comprehensive MAGIC toolkits, innovative nickase-based approaches and anti-CRISPR control systems. These technological innovations collectively address critical limitations in genome editing while opening new experimental possibilities for studying gene function, cellular development, and disease mechanisms in complex biological systems.