Question

• which diseases are candidates for treatment for the crispr - cas9 system.
• how can crispr - cas9 be tailored to target different genes

Explanation:

For the first question: "Which diseases are candidates for treatment for the CRISPR - Cas9 system?"

Diseases with genetic components are candidates. Genetic disorders like sickle - cell anemia (caused by a single - gene mutation), certain types of cancer with genetic mutations driving tumor growth (e.g., some leukemias with specific chromosomal translocations), and inherited retinal diseases (due to mutations in genes related to retinal function) can be targeted by CRISPR - Cas9. It can potentially correct the underlying genetic defects. Also, infectious diseases where the pathogen's genome can be targeted, like some viral infections (e.g., HIV, where the viral DNA integrated into the host genome could be targeted), are candidates.

The CRISPR - Cas9 system uses a guide RNA (gRNA). The gRNA has a spacer sequence that is complementary to the target gene's DNA sequence. To target a different gene, we design a new gRNA with a spacer sequence that is complementary to the new target gene's DNA. The Cas9 enzyme is guided by this gRNA to the specific gene locus. Also, the scaffold region of the gRNA can be optimized for better binding to Cas9 and for stability. Additionally, modifications to the Cas9 protein itself (e.g., using Cas9 variants with different specificities or activities) can be done to tailor the system for different genes, especially in cases where the target region has specific characteristics (like high GC content or epigenetic modifications).

Answer:

Diseases with genetic origins (e.g., sickle - cell anemia, certain cancers, inherited retinal diseases) and some infectious diseases (e.g., HIV) are candidates.

For the second question: "How can CRISPR - Cas9 be tailored to target different genes?"