Using a combination of a parametrized density-functional method for the calculation of the total energy of a given structure and a genetic-algorithm method for the unbiased determination of the structure of the lowest total energy, we have determined structural, energetic, and electronic properties of Si-n,Ge-n, and SinGen clusters with 2-44 atoms. With various specifically developed descriptors, particularly stable clusters are identified, and the structures, overall shapes, bonding patterns, and structural similarities are analyzed and quantified. Finally, the energies of the HOMO and the LUMO are analyzed, and their energy difference is compared with the stability of the clusters.