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As recently as the 18th century, the prevailing theory was called
performation
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performation
is the idea that the egg or sperm contains a miniature infant, or “homunculus,” which becomes larger during development
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development is determined by
the zygote’s genome and molecules in the egg called cytoplasmic determinants
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cell differentiation
is the specialization of cells in structure and function
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morphogenesis
the process by which an animal takes shape
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model organisms
- species that are representative of a larger group and easily studied, for example, Drosophila, Mus musculus and Caenorhabditis elegans
- Classic embryological studies have focused on the sea urchin, frog, chick, and the nematode C. elegans
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Important events regulating development occur during fertilization and the three stages that build the animal’s body, what are the 3 steps?
- cleavage
- gastrulation
- organogenesis
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cleavage
cell division creates a hollow ball of cells called a blastula
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gastrulation
cells are rearranged into a three-layered gastrula
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organogenesis
the three layers interact and move to give rise to organs
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Fertilization brings the haploid nuclei of sperm and egg together, forming a what?
diploid zygote
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The sperm’s contact with the egg’s surface initiates metabolic reactions in the egg that trigger the onset of what?
embryonic development
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acrosomal reaction
triggered when the sperm meets the egg
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acrosome
at the tip of the sperm releases hydrolytic enzymes that digest material surrounding the egg
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polyspermy
- when more than one sperm gets in the egg
- Gamete contact and/or fusion depolarizes the egg cell membrane and sets up a fast block to polyspermy
- Fast block does not exist in mammals
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Fusion of egg and sperm also initiates the what?
reaction
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the reaction induces a rise in Ca2+ that stimulates what to release their contents outside of the egg
cortical granules
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first two steps of the cortical reaction form a fertilization envelope functions as a what?
- slow block to polyspermy
- In mammalian fertilization, the cortical reaction modifies the zona pellucida, the extracellular matrix of the egg
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The sharp rise in Ca2+ in the egg’s cytosol increases the rates of cellular respiration and protein synthesis by the
egg cell
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With these rapid changes in metabolism, the egg is said to be what
activated
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The sperm nucleus merges with the egg nucleus and what happens?
cell division begins
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gastrulation
rearranges the cells of a blastula into a three-layered embryo, called a gastrula, which has a primitive gut
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The three layers produced by gastrulation are called embryonic germ layers which are?
- The ectoderm forms the outer layer
- The endoderm lines the digestive tract
- The mesoderm partly fills the space between the endoderm and ectoderm
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amniotes
Embryos of birds, other reptiles, and mammals develop in a fluid-filled sac in a shell or the uterus
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During amniote development, four extraembryonic membranes form around the embryo which are?
- The chorion functions in gas exchange
- The amnion encloses the amniotic fluid
- The yolk sac encloses the yolk
- The allantois disposes of waste products and contributes to gas exchange
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