Instantons and jumping lines

We study the behaviour under deformation of holomorphic bundles of rank 2 over P1(C). This is then applied to the description of the moduli space Msub(n) of framed SU(2) instantons of charge n; Msub(n) is shown to map to Csup(n), with equidimensional fibers. We use this to provide a stratification of Msub(n) and compute the strata explicitly to codimension 4. This then yields π1(M)sub(n)=Z2, and, for the standard moduli space Msub(n), π1(Msub(n))=0 for n odd, Z2 for n even. (orig.)