The material is organized as follows: the first chapter is devoted to several remarks
on the two basic supersymmetric GUTs - first the minimal SUSY SU(5) is considered
and the main shortcomings are pointed-out in brief, and in the second part these issues
are addressed concerning a general class of SO(lO) models. This provides a natural
motivation to approach and describe shortly the minimal SUSY SO(lO) scheme in the
second chapter. The third chapter is dedicated to a detailed study of the correlations
among the quark and lepton masses and mixing within the framework with dominant
triplet seesaw contribution. An extended framework, a setup with an additional,
quasidecoupled Higgs multiplet transforming as 120 of 50(10), is introduced and studied
in detail in chapter 4. Chapter 5 is devoted to a class of alternative seesaw schemes
emerging in theories with a spinorial 16 in the Higgs sector of SUSY and split-SUSY
SO(lO) GUTs. Finally, a set of Appendices is added to coment on technical points in
the main text.
