Animal Development 2

Animal Development 2 - Animal Development Or: How do you...

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Animal Development Or: How do you get from a single cell to a complete, complex, fully functional, independent, multicellular, heterotrophic organism with only DNA as a guide?
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Well, let’s begin at the beginning… Development begins with fertilization Sperm nucleus orients to chemical stimuli released by the egg The sperm cell binds at a receptor site on the egg surface The acrosome enables the sperm nucleus to enter the egg cytoplasm, where it can fuse with the female nucleus, creating a diploid zygote Why is this a critical step?
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1. Fertilization is critical because: a) It allows species specificity b) Prevents more than one sperm entering egg c) Activates the egg (which is dormant) d) Establishes polarity of the future embryo e) All of the above
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Fertilization “activates” the egg Shift in cytoplasm creates grey crescent
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Dorsal-Ventral Axis Established Early When the cortical cytoplasm shifts, it carries vesicles (red) that inhibit a protein (GSK-3) (blue) that targets β -catenin (orange) for destruction The inhibitor is released into inner cytoplasm, & protects β -catenin, which will become the dorsal cells of the developing embryo
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Yolk ‘lite’ vs ‘heavy’ eggs
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Very heavy yolky eggs: Problem?
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Mammals are a bit different (why ?) The embryo develops from the red mass of cells in the center of the blastocyst, the trophoblast will form the placenta
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As embryo grows, certain groups of cells “fated” to become specific tissue Ectoderm (blue): epidermis of skin, neural ectoderm will become the nervous system
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Animal Development 2 - Animal Development Or: How do you...

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