animal gametogenesis and embryology (chapters 25, 32, 47) what is an animal?
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Animal gametogenesis and embryology (chapters 25, 32, 47) What is an animal? multicellular, heterotrophic, ingest food no cell walls; organisms held together by extracellular matrix; intracellular junctions nervous and muscle tissues are unique distinctive stages of development - PowerPoint PPT PresentationTRANSCRIPT
Animal gametogenesis and embryology(chapters 25, 32, 47)
What is an animal?multicellular, heterotrophic, ingest food
no cell walls; organisms held together byextracellular matrix; intracellular junctions
nervous and muscle tissues are unique
distinctive stages of development
body development regulated by Hox genes
What is a Hox gene?
Contains a “homeobox” that enables it to bind toDNA as a transcription factor (3 -helices)
Remainder of the protein helps determine whichgene it regulates
Some of these gene products help regulate bodypart development (homeotic genes)
So far, homeotic genes have been found only inanimals
Model animals: Drosophila, nematodes
Animals were traditionally classified based onanatomy (body plans) and embryology
New approaches may modify old dichotomies:
I. parazoa vs metazoa (eumetazoa)presence or absence of true tissues
II. radial vs bilateral symmetrycephalizationgerm layers- radiata have two,bilaterals three
Germ layers seen during gastrulation
ectoderm- skin, nervous system
endoderm- (archenteron)- digestive system,liver, lungs
mesoderm- muscles, other internal organs
III. Body cavity (of bilaterials)
acoelomate (flatworms)
pseudocoelomate (rotifers and roundworms)
coelomates- body cavity completely linedby mesoderm tissue
Purpose of body cavity?hydrostatic skeleton in invertebratesgrowth, development and positioning of
internal organs
Protostomes vs deuterostomes
Stages of animal development
fertilization cleavagegastrulation (formation of germ layers)organogenesis
Cleavage distributes cytoplasm of zygoteinto many smaller cells
Cells in most animals have polarityvegetal pole (yolk)animal pole (very little yolk)
yolk is especially prominent in eggs ofbirds, reptiles, many fishes and insects
affects cleavage- incomplete (meroblastic)vs complete (trophoblastic)
Sea urchin gastrulation