This talk will present a systematical semiempirical quantum-chemical study on electron excited states of short DNA duplexes (tri- and tetramers). It has been demonstrated that moderate changes of DNA conformation (within the framework of B-DNA conformation family) might noticeably change its exciton parentage (charge-transfer excitons, normally dark, start to participate in the observed UV-VIS absorption bands). The significance of this finding is discussed.