Transgenic animals produced by pronuclear DNA microinjection Which of the following animals have been reliably produced using direct DNA microinjection into the fertilized egg (pronuclear microinjection)?

Introduction / Context:
Pronuclear microinjection is a classic method for generating transgenic animals by directly injecting DNA into the male pronucleus of a fertilized egg, followed by embryo transfer to a surrogate.

Given Data / Assumptions:

• We are focusing on robust, routine success for a species using this specific technique.
• Other species may require alternative or less efficient methods.

Concept / Approach:
Mice were the first and remain the most reliable model for pronuclear microinjection, with high-throughput pipelines in transgenic cores. While pigs and other mammals have been produced by microinjection, success rates and methods often shifted to SCNT, lentiviral vectors, or genome editing platforms due to efficiency issues. In birds like chicken, the opaque egg and unique embryology make pronuclear microinjection into zygotes impractical; viral vectors or primordial germ cell manipulation are preferred.

Step-by-Step Solution:

Verification / Alternative check:
Most university transgenic facilities list mouse pronuclear injection as a standard service; avian transgenesis uses different routes.

Why Other Options Are Wrong:

• Chicken: transgenesis uses viral vectors or germ cell methods, not pronuclear microinjection.
• Pigs: feasibility exists but less reliable historically; many programs used SCNT or viral vectors.
• All/None: over- or under-inclusive.

Common Pitfalls:
Assuming any animal embryo can be handled like a mouse zygote; species-specific embryology dictates technique choice.

Final Answer:
Mice