T25 X MON810 (OECD identifier: ACS-ZMØØ3-2 X MON-ØØ81Ø-6) maize is an F1 hybrid resulting from the hybridization of the herbicide-tolerant maize inbred T25 (ACS-ZMØØ3-2) with the insect-resistant inbred maize MON810 (MON-ØØ81Ø-6). This stacked maize hybrid is a product of traditional plant breeding, and therefore is not automatically subject to regulation in all jurisdictions as are transgenic plants resulting from recombinant DNA technologies. Certain jurisdictions may request notification in advance of the release of a stacked hybrid, or may request information to conduct an environmental and food safety assessment.  Examples of jurisdictions that require either notification or information about stacked hybrids prior to their release into the environment, and for use in human food and livestock feed are Canada and Japan.<br> <br>The stacked hybrid T25 X MON810 expresses two novel proteins: the PAT protein which confers tolerance to the herbicide glufosinate ammonium, and the delta-endotoxin Cry1Ab which confers resistance to the European Corn Borer and other lepidopterans,   The PAT protein is produced by the <i>pat</i> gene from T25, and the insecticidal protein is produced by the <i>cry</i>1Ab from MON810.  The novel traits of each parental line have been combined, through traditional plant breeding, to produce this new hybrid.  For a full description of each parental line please refer to the individual product descriptions in the crop database for <a href=" dbase.php?action=ShowProd&data=T14%2C+T25&frmat=LONG"><b>T25</b></a> and <a href="dbase.php?action=ShowProd&data=MON810&frmat=LONG"><b>MON810</b></a>.<br>The inserted genes and their gene products have a history of safe use, and have undergone review and approval by several regulatory agencies.  No interactions among the gene products or negative synergistic effects are expected in the stacked hybrid.  The Cry1Ab protein is not an enzyme and therefore does not affect plant metabolism.  The PAT protein has a high affinity for L-Phosphinothricin, the active ingredient in the herbicide glufosinate ammonium.   Cry1Ab and PAT are not expected to interact within, nor affect the metabolism of the stacked hybrid.  <br>Heterosis is expected in F1 hybrids.  An example of heterosis is a substantial increase in yield in the F1 hybrid compared to the parental lines.  The stacked hybrid G21 X MON810 is therefore expected to display heterosis, as would any conventional F1 hybrid.  Heterosis in this hybrid is not expected to be caused by the introduced genes, since the gene products are not expected to interact synergistically.