Question

A sperm that fertilizes an egg carries its mitochondria into the egg’s cytoplasm. However, male-derived mitochondrial nucleoids have completely disappeared within 60 min after fertilization. This experimental observation is most likely due to ________________.

a) The “bottle-neck” inheritance of mitochondria.'

b) The degradation of mitochondrial proteins.

c) The degradation of mitochondrial DNA.

d) The dilution of male-derived mitochondria in the egg’s cytoplasm.

e) The incompatibility of male and female mitochondria.

I chose answer c) The degradation of mitochondrial DNA but my TA told me that the answer was wrong. Was I wrong or was the TA wrong and my answer was actually right? Please explain the answer to me so that I can understand the concept and definitively know what the correct answer is.

Answer 1

The correct answer would be:d) The dilution of male-derived mitochondria in the egg’s cytoplasm.

Reason:The sperm being small in size in comparision to the egg,there occurs a simple dilution of the paternal mitochondria as a result of which limited paternal mitochondria is transmitted to the offsprings.This is also known as simple dilution model according to which the paternal mitochondria DNA being present at a much lower copy number is simply diluted by excess of mitochondrial DNA of the oocyte and therefore is hardly detectable in the offspring.