''MN'' i ''Ss'' aleli se nalaze na blisko vezanim lokusima hromosoma 4; preciznije, klaster MN(S) gena, približne veličine 350 ''kb'' (''5''<sup>''','''</sup>–''GYPA-GYPB–GYPE-3''<sup>''','''</sup>), lociran je na njegovom dugom kraku: ''4q28-q31''.
[[Genetika|Genetička]] kontrola ovog sistema antigena odvija se, dakle, putem dva [[alelogen]]a sa [[hromosom]]a 4 ljudske [[hromosomska garnitura|hromosomske garniture]], koji kodiraju ([[GYPA|glycophorin Aglikoforin]]A i [[GYPB|glycophoringlikoforin B]]). U okviru ovog sistema opisano je čak 46 [[antigen]]a.<ref>Daniels G, Flegel WA, Fletcher A, et al. International Society of Blood Transfusion Committee on Terminology for Red Cell Surface Antigens: Cape Town Report. Vox Sang 2007; 92: 250-3.</ref><ref>Poole J., Daniels G. (2007): Blood group antibodies and their significance in transfusion medicine. Transfus Med Rev 2007; 21: 58-71.</ref><ref>Daniels G. (2002): Human Blood Groups – 2nd Ed. Blackwell Science, Oxford, London.</ref><ref name="isbt">{{cite web|url=http://ibgrl.blood.co.uk/ISBTPages/ISBTTerminologyPages/Table%20of%20blood%20group%20antigens%20within%20systems.htm|title=Table of blood group antigens within systems|author=ISBT Committee on Terminology for Red Cell Surface Antigens|date=|work=|publisher=International Society for Blood Transfusion|accessdate=2010-01-24}}</ref>, među kojima su najznačajniji ''M'', ''N'', '' S'', ''s'' i '' U''. RespektujućiRespektirajući tu činjenicu, u MNS sistemu se javlja šest mogućih fenotipova: ''MS'', ''Ms'', ''NS'', ''Ns'', ''MNS'' i ''MNs''.
