Which of the following statements is true about mitochondrial inheritance?

Mitochondrial inheritance refers specifically to the way organelles called mitochondria and their genetic material are passed down from one generation to the next. In humans and most animals, mitochondria are inherited almost exclusively from the mother. This is because, during fertilization, the sperm contributes very little cytoplasm to the zygote, and thus the organelles, including mitochondria, that are present in the sperm do not significantly participate in the formation of the embryo.

Only the oocyte (egg) contributes the bulk of mitochondria to the embryo, resulting in the maternal inheritance pattern observed for mitochondrial DNA. This is in contrast to nuclear DNA, which comes from both parents.

While mitochondrial genes do play an essential role in cellular respiration and energy production, it doesn't mean that they are always expressed in offspring. The expression can be influenced by many factors, including the developmental stage and the cellular environment.

Thus, the correct understanding of mitochondrial inheritance is that all genes present in mitochondria come from the mother, solidifying the concept of maternal inheritance in mitochondrial DNA.