Who Passed on the Genes?  Key DNA May Be From Dad After All

The Associated Press
W A S H I N G T O N, Dec. 23 — A type of DNA long thought to be inherited only from mothers may be influenced by dad after all, a new analysis indicates. If proven true, scientists may have to rethink some basic beliefs about the timing of human evolution.
Estimates of when humans migrated into Asia and Europe and even the age of “Eve,” the earliest common female ancestor, are based on the changes in mitochondrial DNA, which was assumed to come only from mothers.
But a report in Friday’s edition of the journal Science casts doubt on that assumption.

Changing the Tempo
“Many inferences about the pattern and tempo of human evolution and (mitochondrial DNA) evolution have been based on the assumption of clonal inheritance. These inferences will now have to be reconsidered,” conclude the researchers led by Philip Awadalla of the University of Edinburgh, Scotland.
DNA is the large molecule in each cell that contains the genetic instructions for its development. DNA in the cell nucleus combines material from both mother and father, providing the offspring with traits from both parents.
However, there is also DNA in the mitochondria, the energy-producing portions of the cell, and that had been thought to come from the mother alone.

DNA May Be Combining
Knowing the rate at which DNA tends to change, anthropologists have used this DNA to calculate when human populations separated and estimate how long ago there was a single original human “mother,” whom they call Eve. If it turns out that DNA from mothers and fathers are combining in mitochondria, those dates will have to be recalculated
Awadalla’s report is based on a statistical analysis of how often specific mutations in mitochondrial DNA tended to occur together. The results indicated possible mixing of paternal and material influences in studies of four out of five groups of humans and one group of chimpanzees tested.
Because eggs destroy sperm after fertilization, how male DNA could be arriving in the mitochondria remains a mystery.