Explanation:
There are two main reasons why mitochondrial DNA (mtDNA) is inherited only from the mother:
1. **Transmission during fertilization**: The sperm only gives the embryo genetic material in the form of nuclear DNA during fertilization. During fertilization, the sperm's mitochondria—which have their mtDNA—usually do not penetrate the egg. Because of this, the mitochondria of the embryo, including its mtDNA, are exclusively derived from the mother's egg.
2. **Microbiota location in the egg**: In most animals, including humans, the oocyte (egg cell) provides the majority of the mitochondria in the developing organism. The paternal genetic material is contributed by the sperm cell, which typically does not pass on its mitochondria. As a result, a person's entire mitochondrial DNA comes from their mother's side and is passed down only from the mother.
The study of genetics and evolution will be greatly impacted by this unusual inheritance pattern.
