I know that the D-loop is a DNA complex in which the strands of double helix DNA molecule are separated for a stretch and held apart by a third strand of DNA. Usually, this third strand has a base sequence, which is complementary to one of the main strands and pairs in accordance with it. The third strand then sub sequentially displaces the complementary main strand in the region. Im also aware that D-loops occur in many DNA systems, such as in DNA repair, telomere activity, and in mitochondrial circular DNA molecules. However, my question is why does the D loop only provide information about maternal DNA ancestry?
All the mitochondria of an individual are originating from the mother. This means that if the mother is afflicted by a mitochondrial disease, the offspring will also be affected. This is why the three parent model is being considered in some cases (1).
(1) Pritchard, C. (2014, September 1). The girl with three biological parents. BBC News. From http://www.bbc.com/news/magazine-28986843