How does CRISPR let scientists edit genes?

The answer

CRISPR-Cas9 is a gene-editing tool borrowed from bacteria, which use it as an immune system against viruses. Scientists program a guide RNA molecule to match a specific DNA sequence in the genome. The Cas9 protein then acts as molecular scissors, cutting the DNA at that precise location. The cell's repair machinery can then delete, replace, or insert new genetic material at the cut site. This technology has revolutionized biology and holds promise for curing genetic diseases like sickle cell anemia, which has already been treated in clinical trials.