Debunking a Myth about Sperm's DNA
Travis, John, Science News
Friderun Ankel-Simons and Jim M. Cummins have a biology lesson they think evolutionary biologists should learn. The pair recently chastised fellow scientists for what they contend is a widespread misconception-that one kind of paternal DNA, mitochondrial DNA (mtDNA), does not get into the egg when the sperm fertilizes it.
"How this assumption has spread is startling. It's a scandal because it mis- represents a biological fact," says Ankel-Simons of the Duke University Primate Center in Durham, N.C.
Mitochondrial DNA, which sits inside the energy-producing organelles called mitochondria that roam outside a cell's nucleus, has been a useful tool for evolutionary biologists because many studies have shown that it is inherited only from the mother. For example, mtDNA analysis is at the heart of the con- troversial African Eve hypothesis, which traces human origins to a single woman in Africa (SN: 9/25/93, p. 196).
In the Nov. 26 Proceedings of the National Academy of Sciences, Ankel-Simons and Cummins, a researcher at Murdoch University in Australia, point out that evolutionary biologists almost invariably claim in their research articles and popular books that the paternal mtDNA is not inherited because the sperm's midpiece and tail, where the DNA is located, do not enter the egg. That's false, say the two researchers: Microscopy and DNA analysis show that mtDNA from the sperm's midpiece does appear in the fertilized mammalian egg.
Andrew Merriwether, an evolutionary biologist at the University of Michigan in Ann Arbor, notes that the reasons for maternal-only mtDNA inheritance are unclear and concedes that some of his colleagues may not explain this accurately. Nevertheless, studies have established that paternal mtDNA is so rarely transmitted to offspring that mtDNA analyses remain valid, he says.
"It may get in the egg but it doesn't stay there."
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