Flashcards in Development I Deck (45):
-all the changes in life cycle
-includes embryonic developmental birth/hatching, metamorphosis, etc
species chosen for research -> easily studied
what are the consequences of fertilization?
-restores diploid number
-determines sex (sometimes)
-sperm content activates egg -> start development
external egg structure
plasma membrane with 1+ coverings
-aid in fertilization
-barrier to interspecific fertilization (especially important for species/external fertilization)
steps in fertilization
1. sperm dissolves protective layers around egg
2. sperm binds to egg surface receptors - ensure same species
3. change to egg surface - prevent polyspermy
why are echinoderms used in research a lot?
-easy to work with
-easy to obtain lots of gametes
-external fertilization - easy to observe
name the egg coverings of sea urchins external to internal
jelly coat -> sperm-binding receptors -> vitelline layer -> egg PM
what are the steps in sea urchin fertilization?
1. Ascosomal reaction
2. fast block to polyspermy
3. cortical reaction - slow block to polyspermy
describe the external fertilization in sea urchins
-gametes released into water
-egg jelly coat releases chemicals -> attract sperm (chemotaxes)
acrosomal reaction (sea urchins)
-acrosome in sperm head releases hydrolytic enzymes -> break down jelly coat
-acrosomal process/filaments bind sperm-binding receptor
-recognition triggers plasmogamy - sperm and egg PMs fuse -> sperm nucleus enters egg
preventing polyspermy (sea urchins)
-more than 1 sperm nucleus enters egg (more fatal - abnormal chromosome #)
-2 mechanisms to ensure only 1 sperm enters (fast block ~ 1-3 sec, slow block ~ 1 min)
fast block to polyspermy (sea urchins)
-seconds after membrane fusion: ion channels open in egg PM -> electric "zap" that repels other sperm on egg surface -> prevents addition sperm/egg PM fusion
-lasts ~ 1 min
cortical reaction/slow block to polyspermy (sea urchins)
-also triggered by plasmogamy (membrane fusion)
-vitelline layer separates, hardens -> fertilization envelope-protective layer -> complete block - irreversible, permanent
-requires ~ 1 minute
name the egg coverings of mammals outside to inside
PM -> zona pellucida -> follicle cells
what are the steps in mammal fertilization
1. acrosomal reaction
2. cortical reaction/slow block to polyspermy
fast block to polyspermy in mammals
TRICK QUESTION! THERE IS NO FAST BLOCK TO POLYSPERMY IN MAMMALS
where are eggs fertilized in mammals?
internally - inside oviduct
acrosomal reaction (mammals)
-sperm binds receptor in zona pellucida
-acrosome bursts and release enzyme (helps sperm get through zona pellucida)
cortical reaction/slow block (mammals)
-enzymes catalyze changes in zona pellucida -> ZP hardens -> filters sperm receptors so that no sperm can bind
describe the fertilization envelope in mammals
TRICK QUESTION. THERE IS NO FERTILIZATION ENVELOPE IN MAMMALS
-triggered by sperm binding
-series of metabolic reactions starts, accelerate (onset of embryonic development)
what are the results of egg activation?
-maternal enzymes and proteins activated
-increase protein synthesis - mRNA already present
what is the 2° oocyte triggered by?
for humans, when does the 2° oocyte arrest?
what triggers continuation? what happens as a result?
fertilization. meiosis is complete
when do sea urchin eggs complete meiosis?
-microtubules guide sperm nucleus to egg
-sea urchins ~ 20 minutes after sperm nucleus enters
-humans - several hours
-results in diploid, totipotent zygote
potential to give rise to all cell types
end of fertilization
-when zygote undergoes first division -> embryo
-sea urchins - within 90 minutes
-mammals - 12-26 hours
compare and contrast fertilization in sea urchins and mammals
-echinoderms - in ocean
-fast and slow blocks
-slow block only
-no fertilization envelope
what is the second step in embryonic development and what is formed as a result?
cleavage. single celled zygote becomes a MC embryo
characteristics of cleavage
-very short/no G1 or G2 Phases
-no cell growth
what are the stages of cleavage?
zygote (1 cell) -> 24 hours -> embryo (2 + cells) -> blastula: hallow (blastocoel inside = nothing)*
* at least 128 blastomeres cells of the blastula
radial and indeterminate
mixture of proteins, phospholipids, fats -> food for developing embryo (like endosperm - convergent evolution)
where embryo is
where yolk is
indentation during cytokinesis
how does yolk affect the pattern of division?
amount and distribution of yolk varies between animal groups
-little yolk -> faster, equal cleavage
-lots of yolk -> slower, unequal cleavage
-cleavage furrow passes entirely through egg
-equal division of egg cytoplasm -> equal blastomeres
-cleavage furrow passes entirely through egg
-yolk slows down cytokinesis in vegetal pore -> unequal divisions of egg cytoplasm -> unequal blastomeres (more/smaller blastomeres in vegetal pole, fewer larger blastomeres in vegetal pole)
in what species does unequal holoblastic occur?
species with medium amount of yolk - e.g. amphibians
cleavage furrow does NOT pass entirely through egg (ONLY through pole)
in what species does equal holoblastic occur?
occurs in species with little yolk (e.g. sea urchins, humans)