Chapter 7 Flashcards
describe the cleavage of sea urchins
radial holoblastic
- starts by dividing thru the middle of animal & vegetal poles
what are micromeres?
16 cells only in sea urchins
- found on vegetal pole & form mesoderm
what happens when micromeres are removed from an embryo?
only the ectoderm forms
what happens when micromeres are placed at both poles?
two invaginations form
how do micromeres relate to the Wnt signaling pathway?
contain disheveled
- protects b-catenin from proteases
- allows for transcription of the mesoderm
what would happen if disheveled was in all cells, instead of only micromeres?
only mesoderm would form
what are the three steps of gastrulation in sea urchins?
- ingression
- invagination
- archenteron (cells get pushed to fill blastocoel)
what are regulatory circuits?
turning one gene on has downstream effects
what is the b-catenin circuit?
- b-catenin inhibits gene B
- prevents gene B from inhibiting delta therefore b-catenin indirectly activates delta
describe how a regulatory circuit can activate one gene that magnifies the response of a second gene
- RA can activate Fgf-8 & Shh
- active Fgf-8 activates Shh
- therefore when RA is active, it creates two signals to super activate Shh
why are c. elegans good model organisms?
- fixed lineage pattern (able to follow cells)
- very few cell types & # of cells
- 1mm long -> study millions at a time
- transparent cuticle
- easy to keep alive
- 16 hour development (internal fertilization)
- hermaphrodite
how many cells in a c. elegans larve? how many in an adult?
558
959
how many genes are in a c. elegans? how is they different from humans?
20,000 genes
- no spaces
- no splicing
- no isoforms (one function per protein)
what type of specification do cells in c. elegans have?
autonomous specification
- cytoplasmic determinants decide fate, not neighors (Par-2, Mex-5, PIE-1)
what type of cleavage do c. elegans have?
rotational holoblastic
