SCIENCE WATCH; A Mussel's Genetics Break Inheritance Rules
Published: March 26, 1991
BIOLOGISTS have discovered that a mussel violates a widespread assumption of genetic inheritance.
Analyzing mussels of the genus Mytilus, University of Michigan biologists found that they were an exception to the rule that mitochondrial DNA was passed on to offspring only by the mother. Instead, they found that the DNA was passed on by both parents.
Their findings may make tracking the evolution of various species more difficult. The discovery was reported in the current issue of the journal Science.
Mitochondria are the microscopic power plants of a cell, converting food and oxygen into energy that the cell can use. Mitochondria also carry their own small quotient of DNA, which differs from the more familiar and much larger amount of DNA located in the nucleus, or heart, of the cell. That nuclear DNA determines the overall heredity of an organism, while the genes of mitochondrial DNA serve largely to allow the little power plants to operate.
Since the discovery 25 years ago that all mitochondrial DNA contains 37 genes, scientists have used this type of DNA as a genetic marker. Scientists could track the evolution of different species or differences within a species by comparing their mitochondrial DNA. Tracking the evolution was made easier because this DNA was believed to be inherited only from the mother.
But the new findings will make it more difficult for scientists to track the evolution of these mussels. They will have to determine whether the genetic material came from the father.
The discovery further complicates the work of scientists because the mussel's simplicity promoted its use for research. Dr. Wesley Brown, a University of Michigan biologist who led the research, suggested that the 40,000 scientific papers that have been published studying this mussel must be scrutinized to see whether the new findings affect their conclusions.
And the discovery presents the possibility that some other organisms inherit this DNA from both parents. There is preliminary evidence that fruit flies, clams and other mussels inherit it from both parents, Dr. Brown said.
"Things are no longer neat and convenient," he said.