UPSC Prelims 2021 Q66: Science & Technology – Biotechnology & Genetics
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Answer: (c) Both 1 and 2
Explanation
Mitochondrial Diseases and Inheritance
| Statement | Claim | Verdict | Detail |
|---|---|---|---|
| 1 | Mitochondrial diseases can be prevented by mitochondrial replacement therapy (MRT) before or after IVF | TRUE | Mitochondrial Replacement Therapy (MRT / three-parent IVF) transfers the nuclear DNA of the mother's egg into a donor egg with healthy mitochondria. Done before fertilisation (spindle transfer / MST) or after fertilisation (pronuclear transfer / PNT). UK legalised in 2015; first baby born via MRT in Mexico (2016). |
| 2 | Child inherits mitochondrial diseases entirely from mother | TRUE | Mitochondrial DNA (mtDNA) is inherited exclusively from the mother because the sperm's mitochondria (in the tail) are destroyed after fertilisation. Only the egg's mitochondria pass on. Hence mtDNA diseases follow strict maternal inheritance. |
Both statements are correct. Answer: (c).
Answer: (c) Both 1 and 2.
Why each option is right or wrong
- (a) Incorrect. Statement 2 (maternal-only mitochondrial inheritance) is also a well-established biological fact.
- (b) Incorrect. Statement 1 (MRT prevents transmission) is also true - clinically demonstrated.
- (c) CORRECT. Both statements are true. Mitochondrial Replacement Therapy (three-parent IVF) can prevent transmission (statement 1), and mitochondrial DNA is inherited exclusively from the mother (statement 2) because sperm mitochondria are destroyed post-fertilisation.
- (d) Incorrect. Both statements are scientifically accurate.
Key point
Mitochondrial DNA = inherited only from mother (sperm mitochondria destroyed after fertilisation). Mitochondrial Replacement Therapy (three-parent IVF, 2015 UK) can prevent mitochondrial disease transmission - via spindle transfer (before IVF) or pronuclear transfer (after IVF). Both statements TRUE.
Remember
Both statements are correct: (1) Mitochondrial diseases can be prevented by Mitochondrial Replacement Therapy either before IVF (spindle transfer) or after (pronuclear transfer); (2) A child inherits mitochondrial DNA entirely from the mother because sperm mitochondria are destroyed post-fertilisation. Answer: (c) Both 1 and 2.
Common mistakes
- Confusing mitochondrial DNA (maternal-only) with nuclear DNA (biparental).
- Not knowing Mitochondrial Replacement Therapy legalised in UK (2015) - first legally regulated three-parent IVF programme.
- Assuming genetic diseases are always nuclear. Mitochondrial diseases (Leber's, MELAS, MERRF) follow strict maternal inheritance.
Exam tip
Mitochondrial inheritance: STRICTLY MATERNAL (sperm mitochondria destroyed post-fertilisation). Diseases: Leber's Hereditary Optic Neuropathy, MELAS, MERRF, Kearns-Sayre Syndrome. Prevention: MRT / Three-parent IVF (Spindle transfer OR pronuclear transfer). UK legalised 2015.
Sources
- NHS UK - Mitochondrial Replacement Therapy Guidance
- NCERT Class XII Biology - Chapter 6: Molecular Basis of Inheritance