Download Animal Development - Mrs Winward Kamiakin High School

Animal Development
Chapter 47
Bozeman Tutorial -- Development:
Timing and Coordination (13:41)
Three Stages of Embryonic Development
Embryonic development is a succession of
mitotic divisions which result in the single
cell zygote becoming a complete organism
consisting of trillions of cells.
1. Cell division: increase in the number of
cells.
2. Differentiation: development of
specialized cells that are organized into
tissues and organs.
3. Morphogenesis: physical processes
that give shape to an animal's body and
organs.
Gastrulation
Gastrulation forms a three-layered
embryo with a primitive gut
Three layers produced by gastrulation are
tissues called embryonic germ layers.
Ectoderm (nervous system and outer layer
of skin).
Endoderm (lining of the digestive tract and
liver and pancreas).
Mesoderm (kidneys, heart, muscles, inner
layer of the skin, and most other organs).
“It is not birth, marriage, or death, but gastrulation
which is truly the most important time in your life.”
~~ Lewis Wolpert
Animals are classified on the basis of how
these tissues are organized.
Acoelomates – no body cavity between the gut
and the body wall (flatworms).
Pseudocoelomates – have a body cavity, but
not completely lined with mesoderm
(roundworms).
Coelomates – have a “true coelom”, a body
cavity completely lined with mesoderm; body
cavities may develop differently.
Frog gastrulation
Morphogenesis
In humans, all major organs have developed
from the three germ layers in the first 3 months
of pregnancy.
Development of cells depends on:
1. Polarity of the embryo -- anterior-posterior,
dorsal-ventral, left-right; established by
morphogens (proteins accumulate in cells).
2. Homeotic genes – specify where body parts
will develop; contain a “homeobox sequence”
(Hox, for short) which is present in many life
forms; Hox genes make proteins which turn
other genes on/off during development.