UPSC Prelims 2021 · GS Paper I
Question 66: Science and Technology
In the context of hereditary diseases, consider the following statements :
- 1.Passing on mitochondrial diseases from parent to child can be prevented by mitochondrial replacement therapy either before or after in vitro fertilization of egg.
- 2.A child inherits mitochondrial diseases entirely from mother and not from father.
Which of the statements given above is/are correct?
AnswerUPSC’s answer is (c).
Mitochondrial replacement therapy swaps a mother's faulty mitochondria for a donor's healthy ones. It can be done on the egg before fertilisation (spindle transfer) or on the fertilised egg (pronuclear transfer), so it can be done before or after in vitro fertilisation. Mitochondrial DNA is passed on through the egg, so a child gets mitochondrial DNA from the mother and not from the father. Remember: mitochondria are inherited maternally.
- 1. Spindle transfer works before fertilisation and pronuclear transfer after it.
- 2. Mitochondrial DNA is inherited from the mother through the egg.
How you could have got this
- If you were sure statement 1 is correct, (b) and (d) go: each of them leaves 1 out.
What you needed to know: Spindle transfer works before fertilisation and pronuclear transfer after it.
- Then, if you were sure statement 2 is correct, (a) goes: it leaves 2 out.
What you needed to know: Mitochondrial DNA is inherited from the mother through the egg.
Only (c) is left. This one needs every statement.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Wrong: statement 2 is also correct.
- (b) Wrong: statement 1 is also correct.
- (c) Right: both statements are correct.
- (d) Wrong: both statements are correct.
Worth knowing: Some mitochondrial diseases are caused by faults in nuclear genes, which are inherited from both parents, so statement 2 is arguable; UPSC's key accepts it.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2021, General Studies Paper I, Series A. The paper on upsc.gov.in.