Summary - Events

  • An 'event' is the insertion of a particular transgene into a specific location on a chromosome.  
  • Different events are determined by:
    1. Which transgene is inserted (gene make up)
    2. Where the transgene inserts (which chromosome and location on the chromosome)
    3. The number of copies of the transgene that insert
  • The single cell with the event will divide and differentiate into an entire plant which contains the event (transgene) in every cell. The plant will then be able to pass the event on to all of its progeny through its gamete cells, which carry a copy of the parent's DNA.  
  • Desirable events are rare and most are discarded by the genetic engineer or plant breeder. Reasons for rejecting an event can be summarized as the following:
    1. The transgene inserts into another resident gene that is critical for cell development causing death, codes for a more subtle trait important for cell development negatively affecting growth and yield, codes for a trait important in reproduction preventing the plant from creating offspring.
    2. The transgene inserts into a portion of the chromosome that does not allow for expression of the transgene, or expression that is too low.
    3. The transgene is silenced and cannot be expressed in progeny.
  • Events are passed on to all the cells that divide from the original transformed cell.  
  • Gene silencing occurs when the plant somehow recognizes the new gene(s) and chemically modifies the DNA so it cannot be read for protein synthesis. Usually events where many copies of the transgene have inserted are more prone to silencing over those where only 1 or a few copies have inserted.  
  • Transformation is very labor intensive and expensive. It is a 'hit and miss' procedure requiring thousands and even millions of cells to undergo the process before one is successfully transformed. Typically, more effort is spent trying to transform crops that are the most economically valuable, such as corn and wheat because the return is greater. As a result, progress in those crops is much farther than in less economically valuable crops.
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