During Metaphase the chromosomes can be seen under the microscope and the number, shape and size of chromosomes is different for each species.
The sides we were looking at were those we prepared earlier in the semester, using bone marrow samples we extracted ourselves from the femur of a mouse.
Under the microscope the chromosomes can clearly be seen in metaphase:
We counted the number of chromosomes in each set and looked for breakage in the arms. In 'real life' they do it to map genes, look for mutations in genes, inherited diseases and tumours.