In the process of creating transgenic animals, what technique often involves injecting DNA into the pronucleus of a fertilized egg?

• A. CRISPR/Cas9 editing
• B. Pronuclear injection
• C. Viral transduction
• D. Somatic cell nuclear transfer

Answer: (B)

Injecting DNA into the pronucleus of a fertilized egg is the classic way to generate transgenic animals because it places the foreign DNA right at the single-cell stage, giving it a chance to integrate into the genome as the embryo divides and to be passed to all tissues, including the germline. The pronucleus is the separate maternal and paternal nucleus before they fuse, so delivering DNA at this moment allows early incorporation into the developing genome. After microinjection, the embryo is cultured and then implanted into a surrogate, with the resulting founder potentially carrying the transgene in all cells. This method is specifically about introducing DNA directly into the zygote to create heritable transgenic changes. Other techniques differ in approach: genome editing with CRISPR/Cas9 targets specific sequences in the genome and may be delivered in various ways; viral transduction uses viral vectors to deliver DNA without necessarily targeting the pronucleus; and somatic cell nuclear transfer clones by transferring a donor nucleus into an enucleated egg, not by injecting DNA into a pronucleus.