Due to limitations in oligo synthesis chemistry and other practical considerations, oligos are limited in length to ~200-300 single strand bases with ability to incorporate different type of modification in base, sugar, backbone or incorporate modified base that can confer new and enhanced functionality. On the other hand, synthetic genes can extend to several thousand, double-stranded base pairs. Usually created as a sequence verified clone, the products from these constructs may be the best tool for your research needs.