We have fabricated a device composed of two closely coupled two-dimensional electron systems, one of which resides within an AlAs quantum well at the X point of the Brillouin zone, while the other is contained at the Γ point in the alloy Al0.10Ga0.90As, grown directly below the AlAs. The electronic properties of these two systems are strongly asymmetric: the respective cyclotron masses in the AlAs and the Al0.10Ga0.90As layers, measured in units of the free electron mass, are ∼0.5 and 0.07, while the effective electron g-factors are approximately 7 and 0. With the help of front and back gates, we can confine mobile carriers to either or both of the two quantum wells, as confirmed by magnetotransport measurements.