Q. 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?

[A] 1 only

[B] 2 only

[C] Both 1 and 2

[D] Neither 1 nor 2

Answer: C
Notes:

Why this Question) Scientists at Kyoto University in Japan report a new approach where mutant DNA sequences inside cellular mitochondria can be eliminated using a bespoke chemical compound. (July 2021). 

Ans) c 

Exp) Option c is correct.  

Statement 1 is correct. Mitochondrial replacement therapy (MRT) is a form of reproductive invitro fertilization (IVF) which works on the principle of replacing a women’s mitochondrial DNA (mt-DNA) with the donor’s healthy one. MRT include different techniques like spindles transfer (ST), pronuclear transfer (PNT) or polar body transfer (PBT).   

Pronuclear transfer technique is a significant approach of MRT administered after fertilization, in which two zygotes are raised in vitro.  

Maternal spindle transfer (MST) technique is executed before fertilization is a form of selective reproduction similar to prenatal diagnosis and pre-implantation genetic diagnosis (PGD) 

Statement 2 is correct. Mitochondria are the organelle which contain DNA in circular form, and in animals it is the only organelle in addition to nucleus which contain DNA and gene. The sperm contains very low number of mitochondria and mitochondrial gene. So, in the offspring the mitochondrial genes are inherited from the mother. Thus, a father with mitochondrial gene defect cannot transmit the disease to his offspring.  

Knowledge Base: 

In pronuclear transfer, the mothers egg is first fertilized with the sperm which produces a zygote. The pronuclei of the egg and sperm are then removed from the zygote and inserted into a donor egg that has been fertilized and has had its own nucleus removed. The zygote derived from the donor egg is then implanted into the mothers uterus. So it works before invitro fertilization of women.  

Source:  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7492815/  

https://ncert.nic.in/textbook/pdf/kebt108.pdf  

 Subject) Science