lec 1 zoo

• Embryology vs Developmental Biology
• Embryology focuses on the study of the development of embryos, while Developmental Biology encompasses the broader study of how organisms grow and develop from fertilization to adulthood
• How does the fertilized egg give rise to the adult body?
• How does the adult body produce another body?
• Specific Questions:
• Question of morphogenesis
• Question of growth
• Question of reproduction
• Gastrulation:

  • Migration and displacement of a single layer of surface cells to form three distinct layers
• Patterns of Gastrulation:
• Primary germ layers:

  • Ectoderm = external layer
  • Mesoderm = middle layer
  • Endoderm = innermost layer
• Continuous masses of cells in the 3 primary germ layers become split into smaller groups of cells, each developing into specific organs or body parts
• Growth and Differentiation:
• Involves the growth of organ rudiments and the acquisition of structure and physiochemical properties allowing them to function as adult structures
• Synapomorphic characters of more inclusive taxa develop first than those of less inclusive groups in ontogenetic development
• Refers to the stage between hatching/birth and reaching maturity, where the individual is not fully grown or sexually mature
• Theories on Embryonic Development:
• William Harvey's "Ex ovo omnia" theory

  • Marcelo Malphigi's notes on the microscopic observation of the developing chick embryo
• Preformation:

  • All people who will be born have already been formed, unfolding from the homunculus
  • Originated from Egyptian alchemy
  • Spermists believed in "animalcules" in sperm, while Ovists believed in the future human in the egg
  • Epigenesis:
  • Each person is put together by contributions of each parent, developing from an amorphous mass
  • Originated from Pythagoras and Aristotle
• Karl Ernst von Baer's theory:

  • Embryos of different species resemble each other more closely early in development than as older embryos
  • Embryos of higher species are like embryos of lower species but not like the adults of lower species
  • The course of development of embryos of different taxonomic groups diverge progressively
• Embryological evidence can be used to classify organisms into natural groups and clarify homology

  • Charles Darwin's contributions to embryology