dev bio

• Germ layer formation results in the differentiation of cells into ectoderm, mesoderm and endoderm.
• Most multicellular organisms arise by sexual reproduction
• Some organisms are capable of asexual reproduction
• Some organisms can be propagated through cutting
• Embryology involves the creation of an organism from a fertilized egg
• Development is a slow process of progressive change
• Metamorphosis is the transformation of an organism
• Embryonic development is when a fertilized egg develops into a complete organism
• Developmental biology studies how structure changes over time
• Cell differentiation is the mechanism whereby different sorts of cells arise
• There are more than 200 different specialized cell types in a vertebrate body
• Morphogenesis involves cell and tissue movement that gives the developing organ or organism its shape in three dimensions
• Growth refers to the increase of size and the control of proportion between body parts
• Reproduction involves highly specialized sperm and egg cells
• Some organisms can regenerate every part of their bodies
• Environmental degradation influences the development of many organisms
• Evolution involves inherited changes of development
• Embryogenesis includes stages of development between fertilization and hatching
• Fertilization is the fusion of mature sex cells, the sperm and egg, which are collectively called gametes
• Cleavage is a series of extremely rapid mitotic divisions that immediately follow fertilization
• Gastrulation is when the embryo transforms from a one-dimensional layer of epithelial cells
• Organogenesis is the process of formation of organs from three germ layers
• Spermatogenesis is the production of mature sperm cells
• Oogenesis is the development of mature ova
• Meiosis in males produces four functional sperm, while in females produces one functional ovum and three polar bodies
• Sperm cells have a head, neck/midpiece, and tail for propulsion
• Flagella structure must allow sperm to travel long distances using plenty of energy
• Sperm capacitation is necessary for sperm to acquire the ability to bind the egg
• The egg stores all material for the beginning of growth and development
• Fusion of two gametes creates a new individual with a genome different from both parents
• Recognition of sperm and egg involves chemoattraction, exocytosis, binding, passage, and fusion
• Two mechanisms have evolved for species-specific attraction of sperm and sperm activation
• Acrosome reaction is important for species-specific recognition in fertilization
• Fusion of the egg and sperm cell membrane results in monospermy, which restores the diploid chromosome number
• The fast block to polyspermy is maintained by sodium/potassium pumps in the egg cell membrane
• Polyspermy can be induced if an electric current is applied to artificially keep the sea urchin egg membrane potential negative
• Polyspermy can be induced by applying an electric current to keep the sea urchin egg membrane potential negative
• Fertilization can be prevented by keeping the membrane potential of eggs positive
• The Slow Block to Polyspermy:

  • Slower, mechanical, permanent block
  • Occurs about a minute after sperm-egg fusion
  • Cortical granules fuse with the cell membrane upon sperm entry and release several molecules
  • Mucopolysaccharides released by cortical granules elevate from the cell membrane and are stabilized by crosslinking adjacent proteins
• Calcium as the initiator of the cortical granule reaction:

  • Concentration of free Ca2+ in the egg cytoplasm increases greatly upon fertilization
  • Rise in Ca2+ concentration responsible for the cortical granule reaction comes from within the egg itself
  • A23187 is a calcium ionophore that transports Ca2+ across lipid membranes
  • Placing sea urchin embryos in sea water containing A23187 results in cortical granule reaction and fertilization envelope rise
  • Injecting a Ca2+ chelator into the egg prevents cortical reaction