Symmetric meshing

Dear all,

I'd like to learn if it is possible to have symmetry axis in mesh. I'm working on a 3D model, and the geometry is symmetric in both x and y axis. I'm studying on eigenfrequency analysis and I'd like the mesh to be symmetric in x-axis only.

To be more clear, I don't expect to see symmetric results for all mode shapes of course but when the mode shape is known to be symmetric by analytical means I want to see a more realistic illustration of it.

Thanks,
Utku