Chapter 22 & 23

Chapter 22 & 23 - Chapter 22 23 Developmental...

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Chapter 22 & 23 Developmental Genetics & Cancer Genetics
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Blind Cave Fish Some populations of Mexican tetras are blind after 10,000 years of living in caves Result of increased expression of two genes sonic hedgehog ( shh ) and tiggy-winkle hedgehog ( twhh ) shh was first found in Drosophila and twhh in zebrafish Activates transcription of other genes that leads to apoptosis (cell death) of lens cells Small changes in expression of key genes can have profound effects
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Developmental Genetics Totipotent - ability to develop into any cell type Every cell in a very early embryo is totipotent Value of embryonic stem cells Plant and fungal cells often remain totipotent Animal cells become committed to development into a specific cell type Process called determination that often occurs after the first few cell divisions of the embryo
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Cloning of Animals Cloning experiments with frogs date back to the 1950-1960’s Cloning of a mammal was not considered possible since highly differentiated cells could not be “reprogrammed” to function as single-celled embryo Dolly the sheep (1997) showed that a terminally differentiated mammalian cell retains all original genetic information
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Cloning has been achieved with a variety of animals including sheep, goats, mice, rabbits, pigs, horses, mules, cats and dogs Clones are not genetically identical since the cytoplasmic genes (i.e. mitochondria) come from the donor cell and recipient egg Showed that genetic information is not permanently altered or deleted from the genome during development Therefore, development must requires selective expression of genes How is this process regulated in a complex multicellular organism?
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How Do You Build A Fruit Fly?
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Drosophila Development THREE LARVAL STAGES - PUPAL - ADULT
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Initial Stages of Development SYNCYTIUM - RESULTS FROM NINE NUCLEAR DIVISIONS WITHOUT CELL DIVISION POLE CELLS BECOME THE GERMLINE CELLS ABOUT 6,000 CELLS SURROUND THE OUTER SURFACE OF THE EMBRYO
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Genes For Each Stage of Development SEGMENTATION GENES EGG POLARITY GENES HOMEOTIC GENES Orientation and number of body segments and the identity of each individual segment is established by the time the embryo is 10 hours old TRANSCRIPTS FOR EGG POLARITY GENES ARE PRESENT IN THE EGG PRIOR TO FERTILIZATION - MATERNAL EFFECT GENES
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Development in Drosophila A cascade of genes function to direct the polarity of body formation and the structures associated with individual segment Many code for morphogens , whose concentration gradient affect development of the surrounding regions
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Establishing Dorsal-Ventral Axis DORSAL PROTEIN DORSAL PROTEIN IS DISTRIBUTED THROUGHOUT CYTOPLASM IN EGG PRIOR TO FERTILIZATION. AFTER FERTILIZATION, DORSAL PROTEIN IS ABSORBED INTO THE NUCLEI ON VENTRAL SIDE.
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