• Specific genes expressed in cell during development determine cell type
  • Cell can receive external and internal cues that cause regulation of gene expression by turning genes on/off
  • External: cells receive signals from extracellular environment
    • Adjacent cells: ex: binding of growth factors
    • Environment: temperature can trigger cellular response
  • Internal: signals come from inside cell
    • Cell signals to itself and Cytoplasmic Determinants
  1. Cleavages don’t divide cells equally → cells acquire variations based on orientation of cleavages
  2. Cytoplasmic Determinants: eggs cytoplasm contains RNA, protein, and nutrients encoded by mum DNA
  • Cytoplasmic determinants not dispersed equally which affect embryonic development
    • Cytoplasmic axes and substances unique to each cell may turn genes on or off and set cells down specific path
  1. Embryonic Induction: signaling molecules from embryonic cells cause transcriptional changes in nearby target cells
  • Organizers: cells that exert this influence
  • Cell-cell communication can occur by ligands or interaction between cell surfaces → leads to specific gene expression and cell differentiation
    • Cells closer receive more than cells farther away
  1. Apoptosis: some cells produced during development have temporary role and are deliberately destroyed
  • Ex: during early stages have webbing but later cells undergo apoptosis