This volume is a compilation of 20 articles written by scientists from different parts of the world dealing with various aspects of: repetitive sequences in chromosomes; telomeric sequences and their maintenance by telomerase; chromatin structure and gene activation; centrometric complexity in holocentric chromosomes; translocation frequencies in X and Y chromosomes and evolution of DNA repair mechanisms; cytogenetics of certain groups of animals, such as lepidoptera, fishes and birds; and radiosensitivity as an indicator of predisposition to breast cancer. The molecular genetics of various cancers, such as gastrointestinal, lung, prostate, and bladder are also discussed.