SPARC enables genetic manipulation of precise proportions of cells.

SPARC is an all-genetic toolkit to express effectors in precise proportions of neurons. This method enables imaging of individual neurons and manipulation of neuronal subpopulations. Many experimental approaches rely on controlling gene expression in select subsets of cells within an individual animal. However, reproducibly targeting transgene expression to specific fractions of a genetically defined cell type is challenging. We developed Sparse Predictive Activity through Recombinase Competition (SPARC), a generalizable toolkit that can express any effector in precise proportions of post-mitotic cells inDrosophila. Using this approach, we demonstrate targeted expression of many effectors in several cell types and apply these tools to calcium imaging of individual neurons and optogenetic manipulation of sparse cell populations in vivo.