A pronucleus (plural: pronuclei) is the nucleus of a sperm or an egg cell during the process of fertilization. Pronuclear Transfer is used in mitochondrial transfer techniques. Pronuclear transfer is the transfer of pronuclei from one zygote to another. This technique first requires fertilisation of healthy donated egg (provided by the mitochondrial donor) with the intending male parent sperm. Simultaneously, the intending mother's affected oocytes (an immature egg cell) are fertilised with the intending father's sperm. Both sets of fertilised oocytes (that of the mother and the donor) are allowed to develop to the early zygote stage where the pronuclei are visible. Using micromanipulation equipment, the pronuclei of zygotes formed from donated oocytes are removed within a karyoplast (A cellular nucleus together with a plasma membrane containing a small amount of cytoplasm) and discarded. Therapeutic pronuclear transfer involves the movement of two pronuclei from the affected zygotes (also in the form of a karyoplast), into the enucleated (without a nucleus) healthy zygotes. The resulting zygotes contain nuclear DNA from each of the intending parents and a donor's mtDNA. Hence option (d) is the correct answer.