Developmental Biology Lecture #1

• Embryology is the traditional term for the study of animal development
• Embryo is the developing organism that gives rise to multicellular organisms through development
• Zygote is the fertilized egg that divides mitotically to produce all cells in the body
• Development is continuous, with skin cells being replaced every day and bone marrow producing RBCs every minute
• Animal development is characterized by the differentiation of the fertilized egg into many cell types of the body and the construction of functionally integrated organs
• Development is the route via which an organism goes from genotype to phenotype and can be studied at any level of organization from molecules to ecosystems
• Process of Development:

  • Fertilization is the union of egg and sperm cell in human
• Questions of Developmental Biology:

  • Aristotle was the first known embryologist
  • Our answers to questions must respect the complexity of the inquiry and explain a coherent causal network from gene through functional organs
• Developmental Biology is the discipline that studies embryonic and other developmental processes
• Two Major Objectives of Developmental Biology:

  • It generates cellular diversity and order within the individual organism
  • It ensures the continuity of life from one generation to the next
• Differentiation:

  • A single fertilized egg cell gives rise to hundreds of different cell types
  • This generation of cellular diversity is called differentiation
• Morphogenesis:

  • Differentiated cells are organized into intricate tissues and organs
  • Morphogenesis involves coordinating cell growth, cell migration, and cell death
• Growth:

  • Cells in our body know when to stop dividing to prevent malformations
  • Cell division is tightly regulated to maintain symmetry in body parts
• Reproduction:

  • Sperm and egg are specialized cells that transmit instructions for making an organism from one generation to the next
• Regeneration:

  • Some organisms can regenerate every part of their bodies
  • Stem cells in our bodies can form new structures even in adults
• Environmental Integration:

  • Organism development is influenced by cues from the environment
  • Sex determination in some species depends on environmental temperature
• Evolution:

  • Changes in development create new body forms over generations
  • The study of development is essential for understanding all other areas of biology
• The Cycle of Life:

  • Developmental biology studies the building of organisms from fertilization to hatching
  • Descriptive embryology established a generalizable animal life cycle
• Fertilization is the fusion of mature sex cells
• Comparative Developmental Anatomy:

  • Holoblastic cell division divides the entire egg into smaller cells
  • Meroblastic cell division only uses part of the egg for embryo development
• Embryonic Homologies:

  • Homologous organs have underlying similarity from a common ancestral structure
  • Analogous structures have similarity in function rather than ancestry
• Medical Embryology and Teratology:

  • Between 2% and 5% of human infants are born with observable anatomical abnormalities
  • Birth defects can be caused by genetic malformations, disruptions, and teratogens
• • Cleavage is the dividing of cells
• • Gastrulation is the formation of gastrula
• • Organogenesis is the formation of organs from a set of cells
• • Metamorphosis is changing from one stage to another
• • Regeneration is exhibited by some animals in regrowing body parts
• • Senescence is cell cycle arrest
• Developmental Biology – the discipline that studies embryonic and other developmental processes.
• ·       A single cell, the fertilized egg, gives rise to hundreds of different cell types – muscle cells, epidermal cells, neurons, lens cells, lymphocytes, blood cells, fat cells and so on. This generation of cellular diversity is called differentiation.
• ·       Our differentiated cells are not randomly distributed. Rather, they are organized into intricate tissues and organs.

  ·       During development, cells migrate and die; tissues fold and separate.

  ·       This creation of an ordered form is called morphogenesis, and it involves coordinating cell growth, cell migration and cell death.
• ·       The sperm and egg are highly specialized cells, and only they can transmit the instructions for making an organism from one generation to the next.
• While mammals are generally poor at regeneration, there are some cells in our bodies – stem cells – that are able to form new structures even in adults.
• Evolution involves inherited changes of development.
• Fertilization – fusion of mature sex cells which are collectively called gametes. The fusion of these gametes stimulated the egg to begin development and initiate a new individual.
• Cleavage – a series of extremely rapid mitotic divisions that immediately follow fertilization. During cleavage, the enormous volume of zygote cytoplasm is divided into numerous smaller cells called blastomeres. By the end of cleavage, the blastomere have usually formed a sphere, known as a blastula.
• Gastrulation – happens after the rate of mitotic divisions that immediately followed have slowed down and blastomeres undergo dramatic movement and changes in position. This is when the embryo is said to be in the gastrula stage. Results to embryo containing three germ layers (endoderm, ectoderm, and mesoderm).
• Organogenesis – once the germ layers are established, the cells interact with one another and rearrange themselves to produce tissues and organs.
• Metamorphosis – organism undergoes change to become sexually mature adult.
• Gametogenesis – development of gametes which is usually not completed until the organisms is physically mature.