single cell (zygote) cleaves and grows into multicellular organism with organized body plan with differentiated cell, tissues, and organs (1 cell to a human)
formation of specific 3D structures (tissues and organs)
what was Haekel's philosophy of development?
linear evolution, those less developed forms stop developing earlier in the line
Ernst von Baer philosophy?
1) more specialized thing like hair occurs later in development
2) more specific traits are modifications of more general ones
3) the embryos of a particular species diverge more and more from those of other animals as development proceeds
4) the young embryo of a "higher" animal is not like the adult of a "lower" one
What is differentiation?
development of specialized cell types that have specialized gene proteins
What are the 2 stages of commitment?
1) specification - cells can differentiate autonomously when placed in a neutral environment (can still change their mind if put in different environment)
2) determination - cells can differentiate autonomously even when placed in another region of an embryo
what happens before differentiation?
how can determination occur?
1) segregation of cytoplasmic determinants (morphogenetic determinants) ... assymetric distribution = when the cell divides you get 2 different types of cells because of uneven distribution of granules
2) cell - cell interactions
what is it called when a cell - cell interaction affects cell fate?