All of us have dutifully parroted this one sentence back in high school - ‘Mitochondria are the powerhouse of the cell’. Indeed, one couldn’t sum up mitochondria more succinctly, as that is their precise function in a cell. These tiny, double-layered organelles live happily inside a cell’s cytoplasm, producing energy as and when required. This energy, made in the form of a chemical compound called ATP (Adenosine Triphosphate), keeps the cell up and running.
However, there’s more to mitochondria than just energy production. They have something special, that other cell organelles do not—their own DNA! What makes this so important? Other lowly cell organelles, like Endoplasmic Reticulum, Golgi bodies, lysosomes, do not have any DNA inside them and instead, they are all controlled by the DNA inside the nucleus. Since the mitochondria has its own DNA, it doesn’t take orders from the nucleus! While it’s all fun and games to march on one’s own beat, the mitochondria does face a dilemma when cells reproduce.
The DNA in the nucleus is packed into 46 thread-like structures called chromosomes and each of inherits half of our chromosomes from our father and the other half from our mother. The mitochondrial DNA though, is given to us solely by our mother. Why can’t our fathers do it, you ask? Human sperms have three distinct parts—a head that carries the nucleus, a midpiece that houses the mitochondria and the tail that helps in its movements. When fertilization occurs, it’s only the head of a sperm that fuses with the egg and the tail and midpiece are quite literally, lost. This pattern of inheritance, called as ‘maternal inheritance’ is a widely studied and accepted phenomenon in the scientific community.
But a recent study uproots this understanding of maternal inheritance. It showed evidence of 17 individuals who had mitochondrial DNA from both of their parents! How did scientists not notice this sooner? Turns out, there has always been a bit of a debate among scientist about this topic. There have been reports of bi-parental mitochondrial DNA in other species such as fruit flies and chicken. In humans too, a study from 2002 reported similar findings, albeit in only one individual. With the latest study breathing a new life into the debate, we can hope for explanations that would tell us how exactly this odd, yet intriguing phenomenon is happening right under our noses!