In the context of recent advances in human reproductive technology, "Pronuclear Transfer" is used for

(a) fertilization of egg in vitro by the donor sperm
(b) genetic modification of sperm producing cells
(c) development of stem cells into functional embryos
(d) prevention of mitochondrial diseases in offspring ✓ UPSC's answer

Why the answer is (d)

• Pronuclear transfer is a form of mitochondrial replacement therapy: after IVF, the pronuclei (nuclear DNA) of the parents' fertilised egg are moved into a donor's fertilised egg whose own pronuclei have been removed but whose mitochondria are healthy.

• The child thus inherits nuclear DNA from both parents and mitochondrial DNA from the donor, preventing maternally inherited mitochondrial diseases — option (d).

• The UK approved the technique in 2015; the first such birth was reported in 2016.

• It is not about donor-sperm fertilisation (a), editing sperm-producing cells (b) or stem-cell embryos (c).

• Hence option (d).

Why the other options are wrong

(a) fertilization of egg in vitro by the donor sperm: Donor-sperm IVF is ordinary assisted reproduction, not pronuclear transfer.
(b) genetic modification of sperm producing cells: It does not modify sperm-producing cells.
(c) development of stem cells into functional embryos: It does not turn stem cells into embryos.

Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2020, held on 4 October 2020. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.