The development of an organism or tissue from an egg, seed, spore or other type of progenitor cell is the subject of developmental biology. Developmental biology encompasses the field of embryology - the study of the embryo - and touches upon a number of other disciplines, including cell and molecular biology, genetics and biochemistry. Most research in developmental biology focuses on model biological systems for which powerful tools of manipulation exist, each offering its own advantages. Modern molecular studies on model systems have revealed a remarkable degree of conservation of genes and proteins involved in development between even distantly related organisms, contributing to a new awareness of the relatedness of all species. Research in developmental biology has contributed immensely to our understanding of hereditary diseases affecting human development, and the promise of better treatments or cures for human diseases based on basic research in other species is very exciting.