Transformation Stability

[Peter M.]

Its true that sometimes transgenes can lose activity over generations 
but not the rule. Many if not most lines of transgenic plants are very 
stable well over 3+ generations. The various comercial line approved for 
sale this year being the best examples. What is often seen and not 
understood is the phenomena of co-suppression in which adding more 
copies of a plant gene does not increase expression a great deal. The 
plant seems to down-regulate other copies. This is not seen in animal 
cells. There are other (probably RNA mediated) phenomena such as sense 
suppression and RNA mediated virus resistance that may have similar 
mechanisms.