why the frequency of CRISPR-Cas9 mediated HR is always more than the normal HR in a cell/bacteria?
Hi Muhammad,
As the Cas9 nuclease is introducing a double strand break (DSB) in the DNA the cells will attempt to repair it. The two major means of DNA repair in this scenario are non-homologous end joining which results in indel mutations and homology directed repair. The HDR pathway acts by homologous recombination to identify complementary DNA sequences to use as a repair template for the double strand break. So that the break is repaired precisely.
The Cas9 nuclease will continue to cut at the site it is guided to by its crRNA if the PAM site is not destroyed following cleavage. Therefore increased events of DSBs will result in increased frequency of DNA repair pathways, of which HDR is one.
Hope that answers the question! Feel free to message me if I was unclear.
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