Why tetrahedral complexes do not show geometrical isomerism and square planer complex do not show optical isomerism ?

Tetrahedral complexes do not show geometrical isomerism because the relative position of the all the ligands attached with central metal atom are same with respect to each others. That is all the coordination positions are cis to each other, there are no trans position
                  Squar planer Complexes do not show optical isomerism because they have plane of symmetry. For a compound to be optical isomerism it must not have plane of symmetry.