Gene Silencing,DNA Methylation,Transcriptional Silencing,RNA Transcript

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	Gene Silencing - Frequently, expression of transgenes is suppressed in the subsequent generations of transgenic plants; this is called gene silencing. Gene silencing is often accompanied by DNA methylation of transgenes. In general, higher the number of copies of a transgene, more frequent is their hypermethylation and transgene inactivation. Gene silencing mechanisms are not well understood, but they can be of two types:
(i) transcriptional silencing and (ii) post-transcriptional silencing. Transcriptional silencing is generally due to promoter methylation, while post transcriptional silencing can involve methylation of the coding sequence. The latter does not directly affect transcription. Gene silencing occurs most likely due to RNA transcript degradation.