Question

Should CRISPR be used to alter the human genome to correct genetic mutations? why?

Answer 1

The CRISPR gene editing technique is a very efficient way of disabling genes, by introducing small mutations that disrupt the code of a DNA sequence. CRISPR can also be used to repair genes, but this is much more difficult.

CRISPR is used to delete one of the defective genes, responsible for Hypertrophic cardiomyopathy (HCM), in a number of viable human embryos. The results were promising: Of the 54 embryos that were injected with the CRISPR-Cas9 machinery 18 hours after fertilization, 36 did not show any mutations in the gene (practically no chance of developing the disease) and 13 were partially free of mutations (with a 50 percent chance of inheriting HCM).

To further reduce the chance that only some cells would be changed, modifications in the procedure are ongoing.

CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) techonology is a gene editing method, that targets specific genetic code or DNA at aprticular or damaged position. Through Crispr technology it is possible to correct mutations at precise locations in the human genome, to treat genetic causes of disease. CRISPR system is found in bacteria as a genome editing system and also as defense system against viruses.

When a virus infects the bacteria, the bacteria extracts viral DNA Fragments from invading viruses and use them to create DNA segments known as CRISPR arrays. The CRISPR arrays allow the bacteria to "remember" the viruses. If the viruses attack again, the bacteria produce RNA segments from the CRISPR arrays to target the viruses' DNA. The bacteria then use Cas9 to cut the viral DNA, which disables the virus.

The technology in genome editing involves -

• The spacer sequences (a region of non-coding DNA between genes) are transcribed into RNA sequences which acts as a guide RNA or gRNA. The gRNA contains two RNAs - crRNA that is the transcribed site and is complementaryto the target site of DNA and trcarRNA which identifies the site to be edited.
• The gRNA binds to the target DNA (the segment to be edited) and cas9, a helicase produced by system, cuts the damaged site to produce blunt end.
• The blunt ends are then repaired either by the non-homologous end joining DNA repair pathway (NHEJ) or the homology directed repair (HDR) pathway