Lecture 4 - metazoan development Flashcards
what are the 3 types of ova
1) isolethical - evenly distributed yolk
2) telolethical - conc of yolk in vegetal pole
3) centrolethical - conc of yolk in middle
what type of fertilisation to sea urchins have and why are they useful?
external - used as a model species for looking at development
describe an acrosomal reaction
- sperm touches egg membrane causes series of reactions:
- sodium ions flow into egg
- potential of egg plasma membrane changes to positive
- sets of chain reaction
what does the acrosomal reaction work to do
fast block to polyspermy
describe the cortical reaction
- change in membrane potential results in release of calcium
- cortical granules fuse with plasma membrane
- vitelline layer is polymerised and fertilisation membrane forms
what is the job of the cortical reaction
slow block to polyspermy
what does the change in plasma membrane potential cause
- metabolic changes e.g. protein synthesis
- PH changes
3 main stages of development
1) cleavage (division)
2) gastrulation
3) organogenesis
3 types of cleavage and what types of ova they occur in
1) complete cleavage - isolecithal
2) incomplete cleavage (just on top)- telolecthical
3) superficial (round the outside) - centrolecthical
- different amounts of yolk have varying effects on cleavage patterns
what is inderterminate cleavage
radial - cleavage planes parallel or perpendicular to vertical axis
what is determinate cleavage
spiral - plane of division is diagonal to vertical axis of embryo - embryo twists as it develops
describe a morula and blastula
morula - solid ball of cells
blastula - hollow ball of cells
define gastrulation
when a blastula forms into a gastrula - cells in vegetal pole buckle in forming blastopore and archenteron
what does triploblastic mean
3 body layers
what are the 3 primary germ layers
1) endoderm - gut
2) ectoderm - outer covering
3) mesoderm - muscles, blood system
acoelomate
lack body cavity - solid layer of mesoderm
pseudocoelomate
body cavity only partially lined by mesoderm
coelomate
body cavity lined completely by mesoderm
2 main branches of metazoans
1) protostomes
2) deuterostomes
describe protostomes
cleavage = spiral +determinate coelom = formed by proliferation of cells blastopore = mouth first anus second
describe deuterostomes
cleavage = radial + interdeterminate coelom = formed by pocketing out of archenteron blastopore = anus first
what is the difference between direct and indirect development
direct = no larval stage indirect = larval stage
what types of eggs are likely to be produced in tough and rich environments
tough = lots of yolk + fewer eggs rich = lots of eggs and little yolk
