AML was generated by transducing mTomato+ or YFP+ granulocyte‐macrophage progenitors with retrovirus encoding the MLL‐AF9 oncogene and T‐ALL was generated by transducing fetal liver cells with DsRed‐Notch‐ICN retrovirus. The gene discussed is MLLT3; the disease is acute lymphoblastic leukemia.