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ANIMAL TISSUES AND DEVELOPMENT, blastula embryo taken (from a frog with…

- - - - large array of mutants available
      - large number of offspring
      - short generation time/gestation time
    - - Robust embryos that can be easily manipulated - don't lyse/get crushed
      - large number of embryos
      - external development
    - - relevance to human genome (gene conservation)
      - disease models
      - drug testing
  - - - nematode (Caenorhabditis elegans)
        
        few cells (400 - can be tracked)
        
        transparent body
      - fruit fly (Drosophila melanogaster)
        
        lots of mutants
    - - zebrafish (Danio rerio)
        
        external development
        
        transparent embryo for imaging
      - African clawed frog (Xenopus laevis)
        
        external development
        
        large eggs/embryos
      - Chicken (Gallus gallus domesticus)
        
        large external eggs
      - Mouse (mus musculus)
        
        genetic similarities to humans
        
        genetic modifications
- - - - egg was taken (from frog with pigmented skin) and DNA destroyed by UV radiation
        
        nucleus from blastula cell is injected into 'host' egg
        
        all DNA produced originated from donor nucleus
        
        embryo develops into adult frog
        
        nucleus from early embryo contains all DNA required to produce the many cell types of an adult frog
    - - demonstrates that gene expression is not controlled by losing DNA during early amphibian development
    - - CLONING OF DOLLY THE SHEEP
        
        1996
        
        demonstrated it is possible to clone mammals from an adult differentiated cell type
        
        similar principle to the amphibian experiments but uses a slightly different method
        
        takes a host oocyte (egg that hasn't been fertilised) from Scottish blackface sheep
        
        nucleus removed using extraction with a pipette
        
        donor cell from a Finn-corset sheep
        
        cell placed next to oocyte
        
        electric current used to fuse the egg and donor cell
        
        triggers development with all the DNA coming from the donor cell
        
        1 more item...
    - - any changed which do take place to DNA during development can be reprogrammed to allow development to occur again
        
        how are cells made different during development
    - - legal to produce cloned, very early human embryos for stem cell research