This archival volume is a valuable collection of rigorously reviewed articles by experts in the fields of gene families, DNA, RNA and proteins, to commemorate the passing of a giant of science - Professor Clement L. Markert (1917-1999). In 1959, Clement Markert and Freddy Moller developed the concept of the isozyme, which paved the way for extensive studies of enzyme, protein and gene multiplicity across all living organisms. This important scientific discovery has had a profound influence on the biological sciences for more than 40 years, and has provided the basis for regular international meetings to discuss the biological and biomedical implications of enzyme multiplicity. More recently, this concept has been extended to a wide range of gene families of DNA, RNA, proteins and enzymes.