Question

Briefly explain how both non-homologous end joining (NHEJ) and homology directed repair (HDR) repair mechanisms normally work in the cell, and which types of CRISPR induced mutations can be created by each.

Answer 1

In Non-homologous end joining (NHEJ) pathway, which repairs the double strand breaks which is present in the DNA. It typically utilises the short homologus DNA sequences which is called microhomologoies ( which guides to repair DNA sequences). The microhomologies are usually present in the single- stranded overhangs on the ends of the double-strand breaks. The NHEJ mediated repair of the targeted CRISPR-Cas-9 which induce the DNA that breaks the generated compensatory and deletions which restore the coding frame of the mutated genes.

Homology directed repair (HDR) is the type of mechanism in which the cells to the double strand DNA lesions. The most common form of HDR is the homologus recombination. The HDR mechanism can only be used by the cell where there is a homologus peice of DNA present in the nucleus. Precise form and editing of genomic DNA can be achieved upon the repair of CRISPR-induced DNA double stranded breaks by the homology directed repair (HDR).