  This elementary article introduces easy-to-manage invariants of genus one
knots in homology 3-spheres. To prove their invariance, we investigate
properties of an invariant of 3-dimensional genus two homology handlebodies
called the Alexander form. The Alexander form of a 3-manifold E with boundary
contains all Reidemeister torsions of link exteriors obtained by attaching
two-handles along the boundary of E. It is a useful tool for studying Alexander
polynomials and Reidemeister torsions. We extract invariants of genus one
Seifert surfaces from the Alexander form of their exteriors.
