Mitochondria is a cellular organelle that is used for the purpose of providing energy to the cell.
This cellular organelle has a special property that it has its own DNA and hence, the mitochondrial DNA is transmitted separately from the nuclear DNA, therefore any mutation arising in the mitochondrial DNA will only be inherited if the progeny receives the mitochondria with the mutated mitochondrial DNA.
Further, the mitochondrial inheritance in humans has a special property that only the mother transmits the organelle to the progeny.
Since in the given question the defect in the mitochondrial gene is in the father's mitochondria and in human beings the pattern of mitochondrial inheritance is such that only the mother transmit her mitochondria to the the progeny, the offspring of the man have 0% chance to inherit the defect.
