From: Andy Soos, ENN
Published August 24, 2012 11:42 AM

Paternal Mutations

Mutation is simply defined as "random changes in genetic material". Without mutations and there would be very little change in species or evolution. 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 recently found in the largest study of human genetic mutations to date. The study, based on the DNA of around 85,000 Icelanders, also calculates the rate of human mutation at high resolution, providing estimates of when human ancestors diverged from nonhuman primates. It is one of two papers published this week by the journal Nature Genetics as well as one published at Nature that shed dramatic new light on human evolution.

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“Most mutations come from dad,” said David Reich, professor of genetics at Harvard Medical School and a co-leader of the study. 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.

The researchers used these empirical observations to build a model that was applied to individuals  allowing a way to estimate key parameters of evolution without calibration to the fossil record. It was inhered that the sequence mutation rate is 1.4—2.3 × 10−8 mutations per base pair per generation and that human-chimpanzee speciation occurred 3.7—6.6 million years ago.

Although recent human evolution is difficult to observe directly, some of its impact can be inferred by studying the human genome. In recent years, genetic studies have uncovered many examples where recent evolution has left a distinctive signature on the human genome. The clearest footprints of evolution have been seen in regions of DNA surrounding mutations that occurred fairly recently (typically in the last several thousand years) and confer an advantageous trait, such as resistance to malaria.

Hirschhorn’s team observed, for the first time in humans, a different signature of recent evolution: widespread small but consistent changes at many different places in the genome, all affecting the same trait, adult height.

"This paper offers the first proof and clear example of a new kind of human evolution for a specific trait," said Hirschhorn, who is also a senior associate member of the Broad Institute. "We provide a demonstration of how humans have been able to adapt rapidly without needing to wait for new mutations to happen, by drawing instead on the existing genetic diversity within the human population."

Average heights can differ between populations, even populations that are genetically very similar, which suggests that human height might have been evolving differently across these populations. Hirschhorn’s team studied variants in the genome that are known to have small but consistent effects on height.

The researchers discovered that, in northern Europe, the tall versions of these variants are consistently a little more common than they are in southern Europe. The combined effects of the tall versions being more common can partly explain why northern Europeans are on average taller than southern Europeans. The researchers then showed that these slight differences have arisen as a result of evolution acting at many variants, and acting differently in northern than in southern Europe.

For further information see Mutations or Article.

Figure image by James Sun/Harvard Medical School

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