The ability to create mosaic animals allows the phenotypic analysis of patches of groups of genetically different cells that develop in a wild type environment. In Drosophila, a variety of techniques have been developed over the years to generate mosaics, and in this chapter, I review the techniques that our laboratory has developed. These include the "Dominant Female Sterile" technique which allows the analysis of gene functions to oogenesis and embryogenesis; the "Gal4-UAS" technique which

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... ows the control of where and when specific genes are expressed; and, the "Positive Marked Mutant Lineages" technique which allows clones of cells to express a specific reporter gene.