Question

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: Father with mitochondrial gene defect cannot transmit the disease to his offspring.
Reason R: Mitochondria are the cell organelles which contain D.

• A. Both A and R are correct and R is the correct explation of A
• B. Both A and R are correct but R is NOT the correct explation of A
• C. A is correct but R is not correct
• D. A is not correct but R is correct

Hint:

Mitochondrial diseases are strictly inherited MATERLLY.
An affected mother passes the trait to ALL her children.
An affected father NEVER passes the trait to any of his children.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question assesses materl inheritance patterns of mitochondrial diseases and the presence of extranuclear genomic D within mitochondria.

Step 2: Key Formula or Approach:
Mitochondrial D (mtD) exhibits non-Mendelian, non-nuclear materl inheritance. The zygote receives virtually all of its cytoplasm and organelles from the egg cell (materl parent), while sperm contributes only a haploid nucleus.

Step 3: Detailed Explation:

• Alysis of Assertion A: Because sperm mitochondria are located in the tail/flagellum and are either excluded during fertilization or targeted for ubiquitin-mediated degradation inside the egg, paterl mtD is not passed to offspring. Thus, a father with a mitochondrial gene defect cannot transmit the condition to his children. Thus, Assertion A is correct.

• Alysis of Reason R: Mitochondria are semiautonomous endosymbiotic organelles that harbor their own circular genome (mtD) encoding essential rR, tR, and electron transport proteins. Thus, Reason R is correct.

• Causal Relationship: While Reason R correctly states that mitochondria contain D, it does not explain *why* transmission occurs exclusively through mothers. The actual explation for non-transmission by fathers is materl cytoplasmic inheritance (zygote cytoplasm origiting from the egg). Thus, R is NOT the correct explation of A.

Step 4: Fil Answer:
Both A and R are correct, but R is NOT the correct explation of A.