  In light of the recent solar and atmospheric neutrino data, we investigate
the possibility of having an exactly degenerate spectrum for heavy right-handed
Majorana neutrinos at the grand unification scale. The analysis is performed in
the context of the minimal supersymmetric standard model with unbroken R-parity
and extended with three heavy Majorana neutrino fields in order to implement
the seesaw mechanism. In the absence of a Dirac-type leptonic mixing, the only
source of lepton flavour violation is the right-handed neutrino sector.
Inspired by GUT-motivated relations among the quark, charged-lepton and Dirac
neutrino Yukawa coupling matrices, and after the inclusion of the radiative
effects, we determine the effective neutrino mass matrix at the electroweak
scale. Using then the latest global analyses of the solar and atmospheric data
at 99% C.L., we conclude that, within this framework, the only solar solutions
compatible with the experimental data are the LOW and LMA solutions, being the
latter the most favoured one. At 90% C.L., only the LMA solution is allowed.
