The correct answer is - through the mother.
The mitochondrial DNA, or mtDNA, is the DNA found in the mitochondria, which is practically cellular organelles in the eukaryotic cells which are converting the chemical energy from food into a usable form for the cells, ATP.
Typically, the mitochondrial DNA is inherited from the mother, in most of the multi-cellular organisms. The mechanisms that enable this include simple dilution, degradation of sperm mitochondrial DNA in the male genital tract as well as the fertilized egg, and in some organisms a failure of the sperm mitochondrial DNA to enter the egg.
Despite the differences in the mechanism in which this DNA can be inherited, the end result is the same, a single parent DNA code, found in most of the plants, animals, ad even fungi.
Because of the way this inheritance of DNA works, the mitochondrial DNA is often used for tracing back ancestor further into the past.
