The influence of the gap at Z=70 on the alignment in 161-168Yb is studied using the particle number conserving method.If there is a gap at the Fermi surface,the occupation probability of the[523]7/2 proton orbital does not change as much as when there is no gap.The formation of the plateau of moment of inertia is sensitive to the relative position of the orbital π[404]7/2,π[411]1/2 and π[523]7/2.A third backbending caused by π[541]1/2 is predicted.