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    This is a quote for the textbook 'The attachment of X to the DNA of the gene prevents transcription to mRNA, by stopping RNA polymerase binding. The modification of X affects how tightly the DNA is wrapped around the histones. When wound tightly, the genes are inactive: they cannot be transcribed to mRNA. The gene therefore cannot make protein; it's switched of'

    However, surely the fact X is preventing RNA polymerase from binding means mRNA cannot take place so the gene is switched off anyway, regardless of the DNA being wound tighter. Basically both things individually 'switch the gene off' so do I need to write both things if a related question comes up in an exam? Is it like a step one which leads to step two thing, or , both things switch a gene off so just pick one?

    Thank you
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    Honestly gene expression is very very complicated. Switching genes on and off goes beyond just modifying histones and binding directly to DNA. Those are examples. The question wouldn't be: explain how a gene is switched off, rather it would ask you to name one or two methods. It could be either one or the other, or it could be that it's a cascade of events that leads to both happening. But for the purpose of AS, when a question comes up all you need to say is one way is to modify histones to change how tightly the DNA is bound, and another way is for a protein to bind and prevent RNA polymerase from binding.
 
 
 
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