gestation: carrying one or more embryos in uterus. humans: 266 days rodents: 21 d dogs: 60 d ...
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Gestation: carrying one or more embryos in uterus.
Humans: 266 days Rodents: 21 d Dogs: 60 d Cows: 270 Elephant: 600 days
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Conception: fertilization of egg by sperm Humans: occurs in oviduct Contact of sperm with egg surface: metabolic
rxns within egg that trigger the onset of embryonic development.
Enzymes in acrosome of sperm dissolve outer egg membrane. (lock and key fit: sperm to egg)
Fast block to polyspermy: change in memb. Potential
Slow block: cortical rxn: enzymes released from cortical granules to outside (exocytosis).
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Different species differ in the stage of meiosis the egg has reached at fertilization.
Some: have completed meiosis at time of release from female
Humans: arrested at metaphase of meiosis II. Until fertilized.
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Sperm requires about 6 hours in female reproductive tract … before ready to encounter egg.
Egg: is cloaked by follicle cells (released with it during ovulation)
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HCG: human chorionic gonadotropin: from embryo. Acts like LH Maintain secretion of progesterone and
estrogens by the corps luteum. HCG levels so high they go into urine
(detected in pregnancy test)
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Contains blood vessels of both Mother Embryo
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Organisms development determined by Genome of zygote Neighboring cells (who directs the first
differentiations?)
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Early embryonic cells become different because of Cytoplasmic determinants: maternal substances
found in Unfertilized egg: uneven distribution Heterogeneous cytoplasm of polarized egg
(mRNA, proteins, mitochondria)
Location in embryonic regions with different characteristics. Inner layer or trophoblast Induction: cell stim by nearby cells (gene
expression) Diffusible chemicals OR cell surface interactions
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An animals spatial organization: where organs and limbs are found
Control by induction from nearby tissue
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Cell differentiation: through selective control of Gene Expression.
Cell signaling: Timely communication of instructions telling cells what to do and when to do it.
Morphogenisis: process by which animal takes shape. Differentiated cells end up where they are supposed to.
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Cells developmental potential: range of structures it can give rise to.
Goes down with cells “age” Mammals: zygote cells are totipotent
until the 8 cell stage.
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Cleavage: 24 hours post conception: zygote begins to divide (without dbl cytosol) Blastocyst (blastula), sphere of cells
containing a cavity: made by cleavage(1 wk. post conception). Implants in uterus. Trophoplast: outer layer
Gastrulation: produces 3 layered gastrula
Organogenesis: rudimentary organs from which adult structures arise.
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3 layers
Endoderm: lines tracts, organs Mesoderm: muscle, skeleton Ectoderm: skin, CNS
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Notochord: from dorsal mesoderm: signals the ectoderm to form Neural plate.
Neural plate: dorsal ectoderm: becomes nueral tube. Becomes CNS
In only vertebrates: have neural crest: become, peripheral nerves, teeth skull bones
etc.
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After completion of neural tube: Mesoderm is making 2 tissue layer of
coelom. Somites are beside notochord: they will
become segmented: muscle and vertebrae.
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Adaptations are needed to avoid drying out on land (for all amniotes: reptiles and mammals) amniotes: extraembronic membranes (chorion, amnion, yolk sac)
1. shelled egg of birds and reptiles And monotremes (mammals that lay eggs-
platypus) 2. uterus (eutherians)
Marsupials mammals
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Changes in cell Shape and Position Cell shape: ie neural plate forms neural
tube Reorganize cytoskeleton. Actin fibers
contract. Cell position:
Cells “crawl” within the embryo with cytoskeletal fibers extend and retract.
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Extracellular matrix: secreted glycoproteins outside the plasma membrane.
Direct migrating cells May act as tracks Provide anchorage