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an organism's development is determined by ____ development, which is determined by ______, _______, and _____

gene; the genome, cytoplasmic determinants, induction


process of organism taking shape

acrosomal reaction (sea urchin)

sperm head contacts outer jelly of egg; mcs in egg coat stimulate sperm acrosome to discharge hydrolytic enzymes to digest egg coat; mcs at tip of sperm bind to mcs on egg plasma membrane; ensures that only sperm of species will fertilize; egg and sperm plamsa membranes fuse

cortical reaction (sea urchin)

after sperm binds to egg; vesicles under cell surface in egg discharge chemicals to harden surface of egg; prevent additional sperm from entering; enzymes clip off receptor proteins on outside of egg and any attached sperm

activation of egg (sea urchin)

when sperm bind, signal transduction pathways cause cortical rxn above and cause activation of egg; activation involves increased rates of cell respiration and protein synthesis by egg; can artificially activate an egg by adding calcium or by heat shock; can lead to parthenogenesis

sperm and egg merge after ____ minutes


acrosomal and cortical reaction in mammals

sperm migrates to egg through follicle cells; sperm binds to receptor cells in zona pellucida (ECM of egg); induces acrosomal rxn; acrosom of sperm releases enzymes into zona; enzymes break down EMC so sperm can reach egg membrane; sperm proteins (species specific) bind with cell membrane receptors on egg; cell membranes fuse; sperm contents enter; cortical rxn: zymes released from cortical granules, harden zona pellucida so no more sperm

in mammals, microvilli from egg pull whole sperm into egg cell...

basal body of flagellum form zygote's centriole for first cell division; nuclear envelope disintegrates and chromosomes from egg and sperm share a common spindle apparatus for 1st mitotic division; egg and sperm chromosomes do not join together in one diploid nucleus until after 1st cell division; first cell division occurs 12-36 hours after sperm binding in mammal


rapid mitotic cell division; S (DNA synthesis) and M (mitosis and cytokinesis) phases, no G1 or G2; cells do not grow; embryo stays same size for a few days

polarity of embryo

definite polarity shown by eggs of most animals; due to concentration gradients of mRNA, proteins, yolk, polarity establishes posterior and anterior parts of animal, mammalian eggs have no obvios polarity


hollow ball of cells; called blastocyte in humans; blastocoel develops


cells move to form the gastrula; dramatic rearrangement of cells; transforms blastula into 3 layered embryo with primitive digestive tube

3 germ layers...

ectoderm (developms into nervous system, outer layer of skin); endoderm (inner layer, lines the archenteron (primitive gut), develops into lining of digestive tract, respiratory tract, reproductive tract); mesoderm (develops into kidneys, heart, muscles, skeleton)


archenteron (cavity that forms the digestive tract); opens to the surface through this, will become the anus in deuterostomes

in humans, blastocyst implants in the uterus after _____; it has about ____ cells at this point; the _____(outer layer) helps break down endometrium

7; 100; trophoblast

trophoblast and mesodem will form the _______; other parts formed from the _____

fetal part of the placenta; maternal tissue

4 extrambryonic membranes

chorion (surrounds embryo and all other membranes, contributes to formation of placenta); amnion (encloses the embryo in a fluid filled cavity); yolk sac (encloses a fluid filled cavity, but no yolk; site of early blood cell formation); allantois (develops from an outpocketing of endoderm, incorporated itno umbilical cord; transports materials back and form between mom and baby; disposes of waste)

cell adhesion and EMC help _______ and _____

hold cells together; guide them in their movements

developmental fate of cell depends on...

cytosplasmic determinants in egg (RNA, proteins); cell to cell induction (interactions amoung embryonic cells that induce changes in gene expression): local environments for amniotes; Hox genes involved in limb pattern formation; apoptosis may be involved

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