How can repairing a cut in DNA replace a harmful sequence with a healthy one?

In the context of genetic engineering, repairing a harmful DNA sequence involves precise molecular tools that can target, cut, and replace specific segments of genetic material.1

The process typically utilizes technologies like CRISPR-Cas9, which acts as a form of "genomic surgery." The system uses a guide RNA to direct the Cas9 enzyme to a precise location within the genome. Once the enzyme reaches the target, it creates a cut in the DNA.23

After the DNA is cut, the cell’s natural repair mechanisms are triggered. Researchers can provide a template of healthy DNA alongside the editing machinery. Through a process known as homologous recombination, the cell uses this healthy template to repair the break, effectively swapping the harmful sequence for the desired, healthy one.4

This approach is a cornerstone of gene therapy, which aims to correct mutations that cause genetic diseases. By replacing a defective allele with a functional one, scientists hope to restore normal gene expression and allow the body to produce necessary proteins, potentially curing the underlying condition.1