[en] The Standard model of particle physics is a very successful theory of strong weak and electromagnetic interactions. This theory is perturbative at sufficiently high energies and renormalizable thus it describes these interactions at quantum level. However it has a number of limitations, one being the fact that it has 28 free parameters assuming massive neutrinos. Within the Standard model these parameters can not be explained, however they can be accommodated in the standard theory. Particularly the masses of the fermions are not predicted by the theory. The existence of the neutrino masses can be regarded as the first glimpse of the physics beyond the standard model. In this thesis we have described the quark and lepton masses and mixings in context of non-SUSY SO(10) and four zero texture (FZT). In the four zero texture case the fermion masses and mixing can be related. We have made some predictions using tribimaximal mixing, the near tribimaximal (TBM) mixing and the triminimal parameterization. Our results show that under the TBM the neutrinos have normal, but weak hierarchy. Under near tribimaximal mixing and the triminimal parameterization we find that the neutrino masses in general increase, if the value of solar angle increases from its TBM value and vice versa. It appears that the neutrinos become more and more degenerate for solar angle values higher than TBM value and hierarchical for lower values of solar angle. We also briefly discuss neutrino parameters in the SUSY SO(10) theories. An overview of SUSY SO(10) theories and proton decay is also presented. (orig.)