ADVANCES IN GENETICS increases its focus on modern human genetics and its relation to medicine with the merger of this long-standing serial with MOLECULAR GENETIC MEDICINE. This merger affirms the Academic Press commitment to publish important reviews of the broadest interest to geneticists and their colleagues in affiliated disciplines. Volume 39 of ADVANCES IN GENETICS completes the trilogy of volumes authored by Dr. Igor Zhimulev of the Institute of Cytology and Genetics in Novosibirsk, Russia. This set comprises what is perhaps the most comprehensive collection of volumes dedicated to the study of polytene chromosomes. Volume 39 picks up where the previous two volumes, 34 and 37, left off. It covers the organization of genetic material in the morphological structures of the interphase chromosome, the chromomeres and the interchromomeric regions, and the structural changes occurring during the activation of the chomomeres, the puffs.