In producing transgenic fish, by which method are foreign genes most commonly introduced into fertilized eggs or early embryos?
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AMicroinjection into fish eggs or embryos
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BDelivery by replication-competent viruses only
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CTransfer of whole nuclei (somatic cell nuclear transfer) exclusively
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DAll of these are equally standard for routine transgenesis
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EElectrofusion of adult somatic tissues
Answer
Correct Answer: Microinjection into fish eggs or embryos
Explanation
Introduction / Context:Transgenic fish (e.g., salmon, zebrafish, carp) are made by inserting DNA constructs into early embryos so that the transgene integrates and is transmitted through the germline. Understanding the standard gene delivery route is essential for aquaculture biotechnology and developmental genetics.
Given Data / Assumptions:
- Goal is stable, heritable integration.
- Manipulation occurs at the one-cell or few-cell stage to target germline precursors.
- Common research species include zebrafish with transparent embryos suitable for micromanipulation.
Concept / Approach:Microinjection directly deposits DNA, RNA, or CRISPR reagents into the yolk or cell of early-stage embryos using microneedles. This provides precise timing and location, good survival in skilled hands, and high efficiency for creating founders that transmit the transgene to progeny.
Step-by-Step Solution:
Identify mainstream practice in fish transgenesis: embryo microinjection.Recognize that while viral vectors can be used experimentally, they are less common for routine fish germline transgenesis compared with microinjection.Note that nuclear transfer produces clones, not typical transgenic founders by gene insertion.Select microinjection as the best answer.Verification / Alternative check:Zebrafish community standards (Tol2 transposon systems, CRISPR/Cas9) overwhelmingly rely on microinjection at the one-cell stage, validating this choice.
Why Other Options Are Wrong:
- Viruses: possible but not the dominant approach in fish embryos.
- Whole-nucleus transfer: cloning, not standard for transgene introduction.
- “All equally standard”: inaccurate.
- Electrofusion of adult tissues does not generate germline transmission.
Common Pitfalls:Confusing cloning technologies with transgenesis; overestimating viral use in fish compared with mammalian systems.
Final Answer:Microinjection into fish eggs or embryos