How to add vertices to an object? I somehow managed to delete some of my vertices, as shown in the picture below. Hitting ctrl-z doesn't work.. Is there an easy way of adding those vertices again? I need them to be shaped like the other existing vertices in the sphere.
Use the symmetry:

In edit mode, duplicate all the vertices, and rotate 180° (be sure to have the 3D cursor set at your object's origin), then remove doubled vertices (tune the merge distance if needed).