Mitochondrial inheritance and 3 parent babies

Question 1

General ethical issues

Answer 1

• identity implications – if our characteristics are determined solely by nuclear then might not have a significant impact on the child but it is more than character and physical traits. Even though being born with a mitochondrial disease would have significant impact on the child, they would still have a different life experience, different biography, maybe a different character
• might have uncontrollable, unforeseeable consequence, affecting future generations and modifying genetic heritage in an irreversible way
• should the embryos be used to increase population or should we be using for research to trh and help people through treatments
• why don’t people adopt?
• Cost effective as don’t have to deal with people sad/have mental health issues as they cannot have children?

Question 2

Homoplasmy

Answer 2

A single mtDNA type

Question 3

Heteroplasmy

Answer 3

2+ mtDNA types

Question 4

Maternal spindle transfer

Answer 4

• The spindle of the chromosomes is removed from the donor egg and discarded
• The spindle of the chromosomes is removed from the intending mother’s egg and transferred to the eneucleated donor egg - the intending mother’s egg is discarded
• The reconstructed oocyte contains the intending mother’s nuclear DNA and the donor’s mitochondrial DNA
• The egg is then fertilised

Question 5

Pronuclear transfer

Answer 5

• The intending mother’s egg is fertilised by the intending father’s sperm
• The donor egg is also fertilised by the father’s sperm
• The pronuclei are removed from the zygote of the donor egg and discarded
• The pronuclei are removed from the intending mother’s fertilised egg and transferred to the enucleated fertilised donor egg - the enucleated fertilised egg of the intending mother is discarded
• The reconstructed embryo contains pronuclear DNA from the intending parents and healthy mitochondria from the donor

Question 6

Oogenesis and forming polar bodies

Answer 6

• The primordial germ cell undergoes mitosis in the fetus; at birth the oocyte arrests in prophase of meiosis I
• Once per month, a primary oocyte completes meiosis I and begins meiosis II before arresting at metaphase II
• The first polar body is then produced - the secondary oocyte and polar body are haploid
• The secondary oocyte is ovulated - if fertilised by. a sperm then it undergoes meiosis II and the second polar body is formed

Question 7

Polar body 1 transfer

Answer 7

• The chromosome is removed from the donor egg and discarded
• The first polar body is removed from the intending mother’s egg and transferred to the enucleated donor egg - the intending mother’s egg is discarded
• The reconstructed oocyte contains the intending mother’s nuclear DNA and the donor’s mitochondrial DNA
• The reconstructed egg is fertilised with the intending father’s sperm
• The embryo develops in vitro and is transferred to the womb

Question 8

Polar body 2 transfer

Answer 8

• The intending mother’s egg is fertilised by the intending father’s sperm
• The donor egg is fertilised by the father’s sperm
• The maternal pronuclei from the donor zygote is removed and discarded, leaving a half-enucleated egg
• The second polar body from the intending mother’s zygote is transferred to the half-enucleated egg, which contains the paternal pronuclei and donor mtDNA
• The embryo develops in vitro and is transferred to the womb