What pattern of inheritance would lead a geneticist to suspect that an inherited disorder of cell metabolism is due to a defective mitochondrial gene?

Answer 1

The disorder would always be inherited from the mother because the mother's mitochondrial gene is the only one that survives when the zygote is formed. The gamete from the mother contains all the information. The head of the father's sperm is the only part that survives during fertilization. The tail of the sperm containing the male's mitochondria (an their genes) is lost when the zygote begins development. Thus it is only from the mother that the disorder can be inherited.

Answer 2

A pattern of maternal inheritance, where affected individuals inherit the disorder exclusively from their mother, would suggest a defect in a mitochondrial gene. Mitochondrial genes are inherited from the maternal lineage, as the mitochondria in the egg cell contribute to the offspring's mitochondria. Additionally, a lack of male-to-male transmission and variable expressivity across affected individuals may also point towards a mitochondrial origin of the disorder.