Question map
In the context of recent advances in human reproductive technology, "Pronuclear Transfer" is used for
Explanation
The correct answer is Option 4: prevention of mitochondrial diseases in offspring.
Pronuclear Transfer (PT) is a form of Mitochondrial Replacement Therapy (MRT), colloquially known as "three-parent baby" technology. It is specifically designed to prevent the mother from passing on debilitating mitochondrial DNA (mtDNA) mutations to her child.
- Mechanism: In this process, the mother’s egg is fertilized with the father’s sperm in vitro. The resulting pronuclei (nuclear genetic material) are then removed and transferred into a donor egg that has had its own nucleus removed but retains healthy mitochondria.
- Outcome: The embryo contains the nuclear DNA of both parents (determining physical traits) but the healthy mitochondrial DNA of the donor.
- Distinction: Unlike Option 1, it is not a routine IVF procedure. Unlike Option 2, it does not involve germline modification of sperm. Unlike Option 3, it focuses on disease prevention in live births rather than stem cell research.
Thus, PT is a critical intervention for ensuring that offspring are born free of inherited mitochondrial disorders.
PROVENANCE & STUDY PATTERN
Guest previewThis is a classic 'Science in the Headlines' question. While technically complex, the term 'Pronuclear Transfer' was synonymous with the 'Three-Parent Baby' controversy that dominated science news from 2016 to 2019. If you relied only on static biology books, this was a bouncer; if you tracked major biotech breakthroughs, it was a sitter.
This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.
- Statement 1: In human reproductive technology, is pronuclear transfer used to fertilize an egg in vitro using donor sperm?
- Statement 2: In human reproductive technology, is pronuclear transfer used for genetic modification of sperm-producing (spermatogenic) cells?
- Statement 3: In human reproductive technology, is pronuclear transfer used to develop stem cells into functional embryos?
- Statement 4: In human reproductive technology, is pronuclear transfer used to prevent transmission of mitochondrial diseases to offspring?
- Defines pronuclear transfer as transplantation of the nuclear genome between fertilized eggs (one from the affected woman and one donated by an unaffected woman).
- Indicates the procedure operates on already-fertilized eggs, so it is not a technique that itself fertilizes an egg using donor sperm.
- States that intracytoplasmic sperm injection (ICSI) was performed in patients who underwent pronuclear transfer, showing fertilization (by ICSI) occurs prior to the pronuclear transfer step.
- Does not describe pronuclear transfer as a method that fertilizes eggs with donor sperm; instead fertilization is a separate step (ICSI) before nuclear transfer.
States where fertilisation normally occurs in humans (sperm introduced into vagina, fertilisation in fallopian tube), establishing the basic biological sites and agents (sperm + egg) involved in conception.
A student could use this to contrast natural (in vivo) fertilisation locations with assisted techniques (in vitro) and ask whether pronuclear transfer relates to changing the location or source of gametes.
Describes the female reproductive tract and the normal journey of an egg to the oviduct where sperm encounter it and fertilisation occurs.
One can extend this to note that assisted methods must replicate or replace this meeting of gametes (e.g., IVF) and then consider whether pronuclear transfer is a step that involves donor sperm or manipulation after fertilisation.
Explains that in mammals sperm are deposited inside the female and fertilisation takes place when sperm swim towards the egg, highlighting that fertilisation is an encounter of two gametes.
A student could compare this standard gamete encounter with technologies that perform fertilisation outside the body (in vitro) and then question whether pronuclear transfer is itself the act of fertilisation or a subsequent manipulation.
Mentions freezing of sperm and eggs and biobanks for storage, showing that reproductive cells are handled and stored in assisted-reproduction contexts.
Using this, a student might infer that assisted reproductive technologies manipulate gametes/zygotes and thus investigate whether pronuclear transfer is one such manipulation involving donor gametes.
Notes that blocking the fallopian tube or vas deferens prevents sperm and egg meeting and thus fertilisation doesn't take place, reinforcing that fertilisation requires union of gametes and can be disrupted or bypassed.
A student could extend this to consider that medical interventions can redirect fertilisation (e.g., IVF) and then ask whether pronuclear transfer is an alternative method that uses donor sperm or works after fertilisation.
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