This paper describes a visual interface for analyzing gene expression data generated from multiple biological samples under different controlled conditions. The tasks are to provide a comprehensive overview of thousands of genes under different states and to have an intuitive way to narrow down the set of genes with common behaviors. Our method involves using multidimensional projections and differential charts to help users analyze different sets of data via a web-based interface. Incorporating these charts and other visualization techniques into our final design makes the application accessible to genetics analysts, as demonstrated in the two use cases in plant and cancer researches. We further discuss the feedback from domain experts and the limitations of our approach to accommodate gene exploration tasks.