Question

How are many mitochondrial diseases passed on from parents to offspring?

Question 1 options:

	through the mother only
	by random mutations in the mitochondrial genome
	through the father only
	through an equal distribution from both parents
	through grandparents only

Answer 1

"Mitochondrial diseases" are diseases related to the mitochondrial DNA (mtDNA) - mutations or alterations in the mtDNA. The diseases thus are not related to the genomic DNA, i.e, the DNA present in the nucleus. Now, it has to be kept in mind that the father has XY chromosome and the mother has XX chromosome, so the mother's gamete contains the major portion of the mtDNA rather than the father. This goes on from generations to generations. Thus, the  mitochondrial diseases passed on from parents to offspring through the mother only.

Note: Recent research shows that in few exclusive cases it has been found that the mtDNA from the fathers are inherited by the offsprings by upto 40%, but the predominant idea of mtDNA inherited from mother cannot be still excluded as the statistics for inheritance of father mtDNA cases is very less.