Developments in Plant Genetics and Breeding, 1A: Isozymes in Plant Genetics and Breeding, Part A focuses on the advancements in the processes, methodologies, and approaches involved in the study of isozymes, including its role in plant genetics and breeding. The selection first elaborates on the historical perspectives of plant isozymes, plant genetics, and isozyme systems to study gene regulation during development. Discussions focus on the use of isozyme and similar comparisons to study differential gene regulation, gene preservation, dissemination of cultivars, propagation of cultivars and breeding lines, and studies on the effect of viral infection and hormones on isozyme expression. The text then examines allozymes in gene dosage studies, gene mapping, and plastid isozymes. The manuscript takes a look at the genetics of mitochondrial isozymes, evolution of plant isozymes, and detection of somatic variation. Topics include evolution of isozymes in plants, generation of isozymes, glutamate dehydrogenase, glutamate-oxaloacetate transaminase, and malate dehydrogenase. The text also ponders on enzyme activity staining, isozymic variation and plant breeders' rights, genetic purity of commercial seed lots, and use of isozymes in plant disease research. The selection is a valuable reference for researchers interested in the role of isozymes in plant genetics and breeding.