Humans inherit more than three times as many mutations from their fathers as from their mothers, and mutation rates increase with the father's age but not the mother's, researchers have found in the largest study of human genetic mutations to date.

A study based on the DNA of around 85,000 Icelanders, the largest study of human genetic mutations to date, has found that humans inherit more than three times as many mutations from their fathers as from their mothers and mutation rates increase with the father's age but not the mother's.

In addition to finding 3.3 paternal germline mutations for each maternal mutation, the study also found that the mutation rate in fathers doubles from age 20 to 58 but that there is no association with age in mothers — a finding that may shed light on conditions, such as autism, that correlate with the father's age. 

The study's first author is James Sun, a graduate student in the lab of David Reich, professor of genetics at Harvard Medical School and a co-leader of the study, and they worked with researchers from deCODE Genetics, a biopharma company based in Reykjavik, Iceland, to analyze about 2,500 short sequences of DNA taken from 85,289 Icelanders in 24,832 father-mother-child trios. The sequences, microsatellites, vary in the number of times that they repeat, and are known to mutate at a higher rate than average places in the genome.  They identified 2,058 mutational changes, yielding a rate of mutation that suggests human and chimpanzee ancestral populations diverged between 3.7 million and 6.6 million years ago. 

The findings don't match up with current fossil evidence. The upper bound, 6.6 million years, is less than the published date of Sahelanthropus tchadensis, a fossil that has been interpreted to be a human ancestor since the separation of chimpanzees, but is dated to around 7 million years old. The new study suggests that this fossil may be incorrectly interpreted.

Published in Nature Genetics