9. What pattern of inheritance would lead a geneticist to suspect that an inherited disorder of cell metabolism is due to a defective mitochondrial gene?
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.
Within each cell reside hundreds of tiny gas stations known as mitochondria. These essential organelles generate a large share of the fuel, a molecule called ATP, that cells use to power their biological machinery. There’s a suspicion, admittedly controversial, that problems with these energy-supplying mitochondria contribute to the progression of age-related neurodegenerative illnesses such as Alzheimer’s, Parkinson’s, and Huntington’s diseases, says Douglas C. Wallace of Emory University School of Medicine in Atlanta. In 1993, Wallace and his colleagues reported on comparisons of the mitochondrial DNA of Alzheimer’s patients and that of people without Alzheimer’s, who served as controls. This genetic material, which contains all the instructions necessary for mitochondria to function and replicate, is independent of the DNA found in a cell’s nucleus. Wallace’s group discovered that a particular mutation in mitochondrial DNA showed up in more than 5 percent of Alzheimer’s patients but in less than 1 percent of a random group of people with-out the disease. Studies on animals support the importance of mitochondria in brain disorders. When investigators destroy mitochondria or inhibit the activity of enzymes crucial to mitochondrial function in rats or mice, the rodents develop behavioral or physical attributes of Alzheimer’s, Huntington’s, and Parkinson’s diseases. &emdash; J. Travis
Science News: Aug. 5 • Vol. 148, No. 6