ch. 47 development Flashcards
when does a human embryo show development of distinctive features
5 weeks
fertilization
formation of diploid zygote from a haploid egg and sperm
events at egg surface during fertilization
- sperm penetrate protective layer around egg
- receptors on egg surface bind to molecules on sperm surface
- changes at egg surface prevent polyspermy
polyspermy
entry of multiple sperm nuclei into the egg
acrosomal reaction
acrosome at tip of sperm releases hydrolytic enzymes that digest material surrounding egg
when is acrosomal reaction triggered
when sperm meets the egg
fast block to polyspermy
gamete contact/fusion depolarizes egg cell membrane
what initiates the cortical reaction
fusion of egg and sperm
what happens during the cortical reaction seconds after the sperm binds to the egg
vesicles beneath egg plasma membrane release contents to form fertilization envelope
slow block to polyspermy
fertilization envelope
cortical reaction and fertilization envelope
- requires high concentration of Ca2+ in egg
- reaction triggered by change in Ca2+ concentration
- Ca2+ spread across egg correlates w/ appearance of fertilization envelope
what does the rise in Ca2+ in the cytosol of the egg increase
rates of cellular respiration and protein synthesis
how is egg activated
with the rapid changes in metabolism
where are the proteins and mRNAs needed for egg activation
already present in the egg
where is fertilization in mammals and other terrestrial animals
internal
what must sperm travel through to reach zona pellucida
layer of follicle cells surrounding egg
zona pellucida
extracellular matrix of egg
what does sperm binding trigger
cortical reaction
when does first cell division occur in mammals
12-36 hours after sperm binding
what is fertilization followed by
cleavage
cleavage
period of rapid cell division without growth
what does cleavage partition the cytoplasm of a large cell into
many smaller cells called blastomeres
blastula
ball of cells w/ fluid-filled cavity called a blastocoel
cleavage pattern in frogs and many other land animals
asymmetric due to distribution of yolk
yolk
stored nutrients
2 poles of cleavage pattern
- vegetal
- animal
vegetal pole
has more yolk
animal pole
has less yolk
cleavage furrows in frog
- first 2: form 4 equally sized blastomeres
- third: asymmetric due to yolk in vegetal hemisphere, unequally-sized blastomeres
holoblastic cleavage
complete division of the egg
- in species whose eggs have little or moderate amounts of yolk
- sea urchins and frogs
mesoblastic cleavage
incomplete division of the egg
- in species with yolk-rich eggs
- reptiles and birds
cleavage in Drosophila and other insects
multiple rounds of mitosis w/o cytokinesis
morphogenesis
process by which cells occupy their appropriate locations