Cis-prenyl transferase involved in the synthesis of dolichol, a long-chain polyprenol that is utilized as a sugar carrier in protein glycosylation in the endoplasmic reticulum (ER). Catalyzes the sequential condensation of isopentenyl pyrophosphate (IPP) with farnesyl pyrophosphate (FPP) to produce a polyprenyl pyrophosphate which contains 11 (major) and 12 (minor) isoprene units. (2E,6E)-farnesyl diphosphate + 8 isopentenyl diphosphate = di-trans,octa-cis-undecaprenyl diphosphate + 8 diphosphate Protein modification; protein glycosylation. Lipid metabolism. The synthetic pathway for dolichol synthesis is conserved in Giardia lamblia, even if some of the important enzymes are different from those of higher eukaryotes or remain unidentified. Belongs to the UPP synthase family.