An example of intersectional genetics used to identify two subpopulations of pyramidal neurons in the cortex. A) The intersectional allele consists of four key elements: 1) a broadly active CAGpromoter; 2) an FRT flanked stop cassette; 3) a LoxPflanked mCherry and stop cassette and 4) an intersectional eGFP reporter. B) Delineation of cortical pyramidal neurons expressing Gene A::FLP and Gene B::Cre transgenes. The subset of neurons expressing Gene A will be marked with mCherry upon FLP recombination. The subset of Gene A neurons that also express Gene B will be marked with eGFP expression (intersectional) upon CRE mediated LoxP recombination, and leaving the remaining FLP (mCherry population) as the subtractive population. Importantly, those pyramidal neurons that express Gene B outside the context of Gene A will remain unmarked, since the first stop cassette remains in place.