Homology-directed repair

Definition

Homology-directed repair (HDR) is a precise DNA repair mechanism that uses a homologous template to repair double-strand breaks in DNA. This method is crucial for maintaining genomic stability and is particularly relevant in genome editing techniques, where it allows for accurate insertion of genetic material or correction of mutations using a donor template that shares sequence homology with the target site.

5 Must Know Facts For Your Next Test

1. HDR is more efficient in certain phases of the cell cycle, particularly during the S and G2 phases when sister chromatids are available as templates.
2. The precision of HDR makes it ideal for therapeutic applications, such as correcting genetic disorders or inserting specific genes for gene therapy.
3. In contrast to non-homologous end joining (NHEJ), HDR ensures that the repaired DNA retains the original sequence, preventing mutations.
4. Homology-directed repair can be enhanced by co-delivering a template DNA along with CRISPR-Cas9 components to increase gene editing accuracy.
5. Factors such as the length of homology arms on the donor template can significantly influence the efficiency of HDR in genome editing.

Review Questions

• How does homology-directed repair enhance the precision of genome editing compared to other repair mechanisms?
  • Homology-directed repair enhances precision by utilizing a homologous template to accurately restore DNA sequences at double-strand breaks, unlike non-homologous end joining which can lead to random insertions or deletions. This makes HDR ideal for applications requiring exact genetic modifications, such as correcting mutations in disease-causing genes. By ensuring that the repaired DNA matches the original sequence, HDR minimizes unintended effects on the genome.
• Discuss the role of cell cycle phases in the efficiency of homology-directed repair during genome editing processes.
  • The efficiency of homology-directed repair varies significantly across different cell cycle phases, with S and G2 phases being most favorable due to the presence of sister chromatids that serve as ideal templates. In these phases, cells are better equipped to utilize HDR for repairing double-strand breaks introduced by tools like CRISPR-Cas9. In contrast, during G1 phase, when sister chromatids are not available, HDR efficiency decreases while alternative pathways like non-homologous end joining become more prevalent.
• Evaluate how modifying template DNA design can impact the outcomes of homology-directed repair in genome editing applications.
  • Modifying template DNA design plays a crucial role in optimizing outcomes of homology-directed repair. Key factors include the length and sequence accuracy of homology arms; longer homology arms generally improve HDR efficiency by increasing the likelihood that cells will recognize and incorporate the template during repair. Additionally, incorporating specific sequences within the donor template can direct precise genetic modifications, thus enhancing therapeutic potential. Ultimately, strategic design changes can significantly enhance the precision and efficacy of genome editing strategies relying on HDR.

Related terms

Double-strand break: A type of DNA damage where both strands of the DNA double helix are severed, necessitating repair mechanisms like HDR to restore integrity.

CRISPR-Cas9:

A revolutionary genome editing tool that uses a guide RNA and the Cas9 enzyme to create targeted double-strand breaks, which can then be repaired through mechanisms like HDR.

Template DNA: The donor DNA sequence that provides the necessary information for accurate repair during the homology-directed repair process, ensuring the correct insertion or modification of genes.