The Role of Chromosomes in Development is a collection of papers presented at the 23rd Symposium of the Society for the Study of Development and Growth, held at Amherst, Massachusetts in June 1964. Contributors explore the role of chromosomes in development, highlighting important processes such as the diversification and specialization of cells; the regulation of gene function by the physical state of the chromosome; the functional organization of chromosomes; DNA replication and synthesis; and macronuclear differentiation and subnuclear assortment. This volume is organized into 11 chapters and begins with an overview of chromosome structure and function and the mechanisms underlying the role of the chromosome in embryonic development. This book then discusses the chromosomal DNA replication, the mechanisms of gene modulation, the binding of actinomycin to DNA, and the cytological aspects of DNA replication in higher animals. The next chapters explain localized DNA synthesis in polytene chromosomes; chromosomal RNA and other nuclear RNA fractions; and experimental work probing both genetic and functional mosaicism in the mouse, as well as genetic repression of the R locus in maize. The book also considers how developmental pathways are controlled by genetic mechanisms, and then concludes with a chapter on nuclear differentiation in ciliates and on the phenomenon of subnuclear assortment. This book will be of interest to developmental biologists and embryologists.