The fermion spectrum according to GUTs

Gauge theories seem to be nature's favourite candidate for describing correctly and elegantly the 'observed' (fundamental?) interactions. Among other things gauge theories are supposed to shed light on and improve understanding of many of the age-old 'mysteries' of the observed fermion spectrum. Clearly such hopes have been at least partially fulfilled, especially with the advance of grand unified theories, but still a lot of 'mysteries' remain unsolved. The author reports on the present status of understanding of the fermion spectrum. (14 refs).