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* Genomic imprinting HELP!!
  jayblue22 - 04/02/21 17:55
  Genomic imprinting is a mechanism by which gene expression is regulated. Which of the following correctly defines this mechanism?

a) inhibition of expression by hypomethylation of genomic DNA sites
b) activation of expression by hypermethylaion of genomic DNA sites
c) regulated expression dependent upon parental origins of regulated gene
d) expansion of trinucleotide repeats in imprinted gene resulting in regulated expression
e) activation of expression by hypomethylation of genomic DNA sites
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* Re:Genomic imprinting HELP!!
  iniakin - 04/05/21 23:24
  I`m not some kind of expert, but this is my take on it: methylation makes genes mute. Another words, methylation inhibits gene expression. Imprinting is the result, but methylation is the main mechanism of imprinting.

- Option "a" is wrong, because hypomethylation wouldn`t lead to inhibition of gene expression. It would lead to the opposite. It would activate the genes, since there`s a low activity of methylation.
- Option "b" is wrong, because hypermethylation would lead to inhibition of gene expression, NOT their activation.
- Option "e" is wrong as well, because imprinting is not about activation of gene expression, though the sentence itself is correct.
- Option "d" is wrong, because "expansion of trinucleotide repeats" in general causes trinucleotide repeat expansion disorders. For instance, excessive amount of CGG repeats in FMR-1 gene leads to excessive hypermethylation of FMR-1 gene, since methylation happens at CpG islands ("p" represents the phosphate bond between C-G), eventually causing Fragile X Syndrome. The main mechanism of imprinting is methylation, NOT trinucleotide repeat expansion, this is wrong. Even more, why would you like to add these trinucleotide repeats in the gene, which is already imprinted? Excessive amount of trinucleotide repeats causes disorders via DNA slippage mechanism, so it would be better to avoid this mechanism whenever it`s possible in our bodies, I think.

By using this logic, we`re getting to the right answer and this is option "c". I`d like to notice that imprinting is a completely normal process.
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