13. Which one of the following techniques is generally used to produce transgenic animals?
(1) Processed mRNA containing only exons are introduced into blastocyst stage embryo.
(2) Entire foreign nucleus is introduced in enucleated unfertilized egg.
(3) Desired DNA is micro injected into fertilized eggs followed by implantation of embryo in a foster mother.
(4) c-DNA of desired gene is introduced into animal embryos and implanted in a foster mother
The correct technique is (3) Desired DNA is microinjected into fertilized eggs followed by implantation of embryo in a foster mother.
Option-wise explanation
(1) Processed mRNA into blastocyst
Introducing processed mRNA into a blastocyst would yield only transient expression; mRNA is not copied into the genome and would be degraded after a short time.
This does not create a heritable transgenic animal.
(2) Entire foreign nucleus into enucleated unfertilized egg
This describes somatic cell nuclear transfer (cloning), where the donor nucleus already carries the genetic modification.
While this can produce genetically modified animals, it is not the general textbook method for making transgenics and is more often described in the context of cloning (e.g., Dolly).
(3) DNA microinjection into fertilized eggs + implantation – correct
The classical method to produce transgenic mice and many other animals is:
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Isolate fertilized eggs (zygotes).
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Microinject the desired DNA (often into the male pronucleus).
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Culture briefly and implant the embryos into a pseudopregnant foster mother.
If the DNA integrates into the zygotic genome, the resulting offspring carry the transgene in their germline, making them true transgenic animals.
(4) cDNA into embryos and implantation
Simply introducing cDNA (without ensuring genomic integration) is again likely to give transient, non‑heritable expression.
For stable transgenesis, the DNA construct must integrate into chromosomal DNA; the option as stated does not specify the required integration method.
For routine production of transgenic animals, the widely accepted and “generally used” technique is therefore microinjection of the desired DNA into fertilized eggs followed by implantation into a foster mother (option 3).
