Spiral galaxies are axi-symmetric objects showing 2D-chirality when projected
onto a plane. Features in common with tetrahedral molecules are pointed out, in
particular the existence of a preferred chiral modality for genetic galaxies as
in aminoacids and sugars. Environmental effects can influence the intrinsic
chirality of originally isolated stellar systems so that a progressive loss of
chirality is recognised in the Hubble morphological sequence of galaxies.Comment: 17 pages, 4 figure