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

Answer: D. PRONUCLEAR TRANSFER is used for PREVENTION OF MITOCHONDRIAL DISEASES IN OFFSPRING. PRONUCLEAR TRANSFER (PNT) is a form of MITOCHONDRIAL REPLACEMENT THERAPY (MRT), an advanced assisted reproductive technology developed to prevent the transmission of MITOCHONDRIAL DISEASES from mother to child. MITOCHONDRIAL DNA (mtDNA) is inherited EXCLUSIVELY FROM THE MOTHER. Mutations in mtDNA cause a range of serious inherited disorders (Leigh syndrome, MELAS, MERRF, Leber hereditary optic neuropathy) that affect tissues with high energy demand, especially brain, muscle, heart and kidneys. These conditions are often progressive and incurable. PRONUCLEAR TRANSFER PROCEDURE: 1. Both the affected woman's egg AND a healthy donor egg are fertilised by the father's sperm via IVF. 2. SHORTLY AFTER FERTILISATION, while both fertilised eggs are at the pronucleus stage (before the male and female pronuclei have fused), the PRONUCLEI (nuclear DNA from sperm and mother) are removed from the AFFECTED COUPLE'S ZYGOTE. 3. These pronuclei are TRANSFERRED INTO THE DONOR ZYGOTE (whose own pronuclei have been removed) which has HEALTHY MITOCHONDRIA. 4. The reconstituted zygote, with the affected couple's nuclear DNA and the donor's healthy mitochondria, develops into an embryo and is transferred to the mother's uterus for pregnancy. The resulting child has NUCLEAR DNA FROM BOTH PARENTS (around 99.9 percent of the genome) and a small amount of MITOCHONDRIAL DNA FROM THE DONOR (around 0.1 percent of the genome). This is sometimes informally called 'three-parent IVF', though the mitochondrial contribution is genetically minor. A related technique is MATERNAL SPINDLE TRANSFER (MST), performed BEFORE fertilisation: the nuclear spindle (with chromosomes) is moved from the affected woman's unfertilised egg into a donor egg with healthy mitochondria, which is then fertilised. REGULATORY STATUS: The UNITED KINGDOM legalised MRT (including pronuclear transfer) for clinical use in 2015 (the world's first national regulatory approval for the technique). The first MRT babies have been born in the UK. Other countries (Mexico, Greece) have also reported births. India has not approved MRT for clinical use as of the early 2020s. Why other options are WRONG: (A) IVF with donor sperm is conventional in vitro fertilisation, not pronuclear transfer. (B) Genetic modification of sperm-producing cells (spermatogonial stem cell editing) is a separate area of research, not pronuclear transfer. (C) Development of stem cells into embryos (synthetic embryos, blastoids, etc.) is a different field, not what pronuclear transfer refers to. Source: NCERT Class 12 Biology 'Reproductive Health' and 'Principles of Inheritance and Variation'; The Lancet on Mitochondrial Replacement Therapy; UK Human Fertilisation and Embryology Authority (HFEA) MRT framework.