Many of my readers are probably familiar with the fact that we inherit our mitochondria, those little power houses of the cell, from our mothers. In fact, the mitochondria of sperm are marked with proteins for destruction long before the sperm ever reaches the egg.
As part of their respiratory system, mitochondria produce reactive oxygen species (ROS), which are potentially harmful free radicals that can result in mutations and damage to the fatty membranes of the cell. In order to prevent this damage, the cell either produces antioxidants or borrows them from the organism’s diet, which are then used to detoxify the ROS.
Interestingly, estrogen, one of the major female-associated hormones, is a key driver of antioxidant production. This means that females are able to handle a higher ROS load than males. Females, therefore, benefit from a protective effect and even when mutations do occur in mitochondrial DNA (mtDNA), they are less likely to experience ill effects than males with the same mutations. This is because estrogen also helps prevent the cell from committing suicide when it accumulates detrimental mutations. (Sadly, this also is the mechanism that drives tumor formation in some female-associated cancers.)
Ultimately, this means that males are at a higher risk for mitochondrial disorders because mtDNA mutations in females may be relatively silent due to the protective mechanisms that are a result of their sex. This tendency is known as the “Mother’s Curse” and has been implicated in a variety of conditions, including autism.
In spite of this propensity, maternal patterns of mitochondrial inheritance are generally more protective than if they were inherited at random or even paternally inherited. Case in point: there are certain diseases such as mitochondrial myopathy that are associated with paternal inheritance of the mitochondria. Since male mitochondria are more vulnerable to damage from ROS, their mitochondria tend to be worse for wear.
It therefore makes sense that evolution has selected the mitochondria with the (potentially) least amount of damage in order to pass on to future generations. And for these reasons, we are more closely related to our mothers than to our fathers.