Final answer:
The correct answer to the question is 'c', which states that accurate DNA sequences flanking the target gene are required for homologous recombination in gene targeting or disruption constructs. This facilitates only the desired genetic modifications, often visible through phenotypic changes such as antibiotic resistance or reporter gene disruption.
Step-by-step explanation:
The question asks whether targeting constructs or disruption constructs require significant knowledge of the sequence of the target gene. The correct answer is c. DNA sequences flanking the target gene must be accurately known and incorporated into the targeting construct to facilitate precise homologous recombination at the intended site. This ensures that the changes made will affect only the targeted gene and not other parts of the genome. For example, with antibiotic resistance markers, such as those used for ampicillin resistance, bacteria that have successfully incorporated the plasmid with the desired genetic alterations can grow in the presence of the antibiotic, indicating successful gene targeting.
In recombinant DNA technology, this process involves cutting both foreign DNA and a plasmid with the same restriction enzyme and allowing them to anneal. If the insert disrupts a reporter gene, such as lacZ, which metabolizes X-gal, this can alter the phenotype of the host cells (e.g., the color of the colonies), making it easier to identify those with the recombinant plasmid. Accurate gene targeting, particularly in applications like CRISPR/Cas9, requires careful design of the guide RNA to match the target sequence to induce site-specific genetic modifications.