Homologous recombination is the correct technique for inactivating a gene by directly altering its DNA sequence. This method precisely targets and replaces or disrupts the gene’s coding region. It stands out among options as the only one that modifies genomic DNA itself.

Correct Answer

1. Homologous recombination precisely inactivates genes by altering the DNA encoding them. It involves designing a DNA construct with sequences homologous to the target gene, flanked by selectable markers or disruptive elements. Cellular machinery then integrates this construct via recombination, replacing the functional gene with a non-functional version, commonly used in knockout models.​

Option Breakdown

• Homologous recombination: Uses targeted DNA replacement to disrupt gene function at the genomic level, essential for stable, heritable inactivation in research like creating knockout mice.

• Antisense nucleic acid block: Employs complementary RNA or DNA oligos to bind target mRNA, blocking translation or triggering degradation via RNase H, but leaves DNA unchanged.

• Antibody microinjection: Delivers antibodies into cells to inhibit protein function post-translation, without any DNA or RNA alteration.​

• Introduction of dominant inhibitory mutant: Overexpresses a mutant protein that interferes with the wild-type version, acting at the protein level without modifying DNA.​

Molecular Biology Applications

Homologous recombination revolutionized gene knockout studies since the 1980s, enabling precise functional genomics. Unlike transient methods like antisense, it ensures permanent inactivation passed to daughter cells. This technique underpins CRISPR advancements, though traditional HR remains key for complex edits. For exams, distinguish DNA-level (HR) from RNA/protein-level methods.​