Fate of Cells The developing embryo undergoes morphogenesis in order to create different tissues and organs through cleavage, gastrulation, and organogenesis Morphogenesis… changing of form, shape, or function Cleavage… pinching off to form 2 structures or a division within a structure Gastrulation… forming a cavity Organogenesis… specialization of tissue for a function

Cell Differentiation Cells are totipotent in the first 16 cells of the of the blastocyst Potency is reduced with each cell specialization there after Initial differentiation due largely to uneven distribution of cytoplasmic determinants in the yolk of the egg Egg is polarized creating heterogeneous cytoplasm Cleavage creates uneven distribution of mRNA and asymmetrical cell division Process of induction causes the specialization of most cells Created through contact via diffusible chemical signals

Fate Mapping Manipulation of embryonic cells to determine the lineage of cells from the first cleavage event

Cellular Asymmetries Axes of body plan Anterior-posterior, ventral-dorsal, right-left Establishes bilateral symmetry 1st step in morphogenesis and tissue/organ formation Bicoid region of flies Determined by melanin in the yolk during oogenesis Gravity helps determine anterior/posterior axis in chicks pH determines ventral/dorsal…marked by the gray crescent in many embryos