- The following statements are made regarding developing a transgenic mouse:
A. The transgenic mouse thus born will be a homozygous transgenic animal and can be
maintained by crossing with another transgenic animal.
B. The fertilized transgenic eggs are allowed to develop in vitro.
C. The desired gene is preferably microinjected in male pronucleus after sperm entry in oocyte.
D. For best efficiency, the desired gene is always microinjected in the male gametes and then they are allowed to fertilize the female gametes.
E. Blastocyst stage embryos are transferred to the uterus of hormonally prepared mother.
F. The fertilized eggs are collected from specific strain of mouse.
G. The female mouse of specific strain is super ovulated, oocytes are collected and allowed to
fertilize in vitro.
Choose the combination of statements arranged in the correct sequence for developing transgenic mouse.
(1) G→C→E (2) F→B→A
(3) G→D→A (4) D→F→B→AThe correct sequence is G → C → E, so the answer is option (1).
Understanding each statement
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G. “The female mouse of specific strain is super ovulated, oocytes are collected and allowed to fertilize in vitro.”
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This is the first step: obtain many fertilized eggs (zygotes) from a defined genetic background.
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C. “The desired gene is preferably microinjected in male pronucleus after sperm entry in oocyte.”
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This is the core transgenesis step: DNA is injected into the male pronucleus of the fertilized egg, where integration into the genome can occur before the first cleavage.
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E. “Blastocyst stage embryos are transferred to the uterus of hormonally prepared mother.”
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After microinjection and brief culture, embryos reach blastocyst stage and are implanted into a pseudopregnant foster mother to develop to term.
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Together, G → C → E describes the standard workflow for producing transgenic mice by pronuclear microinjection.
Why the other options are incorrect
(2) F → B → A
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F: “Fertilized eggs are collected from specific strain of mouse.” – could be an early step.
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B: “Fertilized transgenic eggs are allowed to develop in vitro.” – vague, omits the actual microinjection step.
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A: “The transgenic mouse thus born will be a homozygous transgenic animal…” – incorrect; founders are usually heterozygous, and homozygotes are obtained only after further breeding.
Hence this sequence is biologically inaccurate.
(3) G → D → A
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D: “Desired gene is always microinjected in the male gametes and then they fertilize female gametes.” – describes sperm‑mediated gene transfer, not the standard pronuclear method; “always” is wrong.
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A: again incorrectly assumes the first transgenic mouse is homozygous.
So this sequence is not the accepted method.
(4) D → F → B → A
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Starts with the incorrect D (male gamete injection), followed by F and B without explicit pronuclear injection, and ends with A, which misstates zygosity.
Therefore, only option (1) G → C → E correctly lists the essential steps in order for developing a transgenic mouse via pronuclear microinjection.
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