1. Introduction

• Developmental biology studies embryonic and other developmental processes
• Embryology is a key subdiscipline of developmental biology
• Embryonic development towards adult form is not linear
• A single fertilized cell develops into all of the cells in the individual
• Cells in embryos can direct their fate based on positional cues and instructions in their genes
• Embryos build themselves progressively through development
• Basic Principles of Development:

  • Cleavage: Cell Division in multicellular organisms
  • Gastrulation: Formation of 3 Germ layers
  • Organogenesis: Cell differentiation into Blood, Muscle, Nerves, etc.
  • Growth: Maturity
  • Morphogenesis or Developmental Mechanics: Involves Cell adhesion, shape, movement, proliferation/death, and extracellular materials
• Developmental events are controlled by differential gene expression
• Major developmental defects occur in approximately 3% of live births
• Developmental biology is the study of the process by which organs grow and develop
• Developmental biology studies genetic control of cell growth, differentiation, and morphogenesis
• Developmental biology is the causal analysis of cellular mechanisms driving growth, pattern formation, and morphogenesis
• Developmental biology studies how animals and plants grow and develop, synonymous with ontogeny
• Questions in developmental biology revolve around understanding biochemical changes during physiological transitions between developmental stages
• Developmental Biology is defined by questions of Differentiation, Morphogenesis, Growth, Reproduction, Evolution, and Environmental Integration
• Differentiation involves the development of a single, pluripotent cell into a complete organism
• Morphogenesis studies how differentiated cells move and reorganize to generate functional organisms
• Growth questions the limiting factors for cell division and rates of mitosis in embryos
• Reproduction involves gametogenesis and interaction of gametes at fertilization
• Evolution studies the evolutionary relationships between groups of organisms
• Environmental Integration shows how early development of organisms is influenced by environmental cues
• Comparative Embryology, Evolutionary Embryology, Teratology, and Mathematical Modeling contribute to the study of development
• Early "Embryologists" like Aristotle, William Harvey, and Marconi Malpighi made significant contributions to embryology
• Aristotle considered basic developmental questions about the existence and growth of developing organisms
• Aristotle discussed Epigenesis versus Preformation in embryonic development
• Preformation theory suggests the organism is preformed in the sperm or egg and grows larger, while Epigenesis theory states the organism develops in a stepwise fashion from an unorganized state
• Aristotle believed the embryo was formed from menstrual blood interacting with a male factor present in the semen
• Aristotle believed that the embryo was formed from the menstrual blood interacting with a male factor in the semen
• His observations supported the concept of epigenesis
• Malpighi found embryonic structures in unincubated eggs left in the warm sun of southern Italy during the summer months
• Malpighi's observations spurned the preformationist ideas
• Preformationists believed in tiny preformed beings present in the gamete, with even tinier beings within their embryonic germ cells
• Nicolas Hartsoeker, a Dutch mathematician and physicist, was a spermist preformationist
• Charles Bonnet, a Swiss philosopher, was an Ovist preformationist
• William Harvey, physician to King Charles I of England, explained blood circulation and published Essays on the Generation of Animals
• Rene Descartes, a philosopher, introduced the famous phrase "Cogito ergo sum"
• Pierre Maupertuis, a French mathematician and biologist, introduced the theory of survival of the fittest
• Christian Pander visualized epigenesis of embryonic germ layers
• Ernst von Baer described the notochord, discovered the mammalian egg, and proposed 4 laws of development
• Heinrich Rathke described pharyngeal arches and skull formation