The high spontaneous mutation rate: is it a health risk? - PubMed (original) (raw)

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The high spontaneous mutation rate: is it a health risk?

J F Crow. Proc Natl Acad Sci U S A. 1997.

Abstract

The human mutation rate for base substitutions is much higher in males than in females and increases with paternal age. This effect is mainly, if not entirely, due to the large number of cell divisions in the male germ line. The mutation-rate increase is considerably greater than expected if the mutation rate were simply proportional to the number of cell divisions. In contrast, those mutations that are small deletions or rearrangements do not show the paternal age effect. The observed increase with the age of the father in the incidence of children with different dominant mutations is variable, presumably the result of different mixtures of base substitutions and deletions. In Drosophila, the rate of mutations causing minor deleterious effects is estimated to be about one new mutation per zygote. Because of a larger number of genes and a much larger amount of DNA, the human rate is presumably higher. Recently, the Drosophila data have been reanalyzed and the mutation-rate estimate questioned, but I believe that the totality of evidence supports the original conclusion. The most reasonable way in which a species can cope with a high mutation rate is by quasi-truncation selection, whereby a number of mutant genes are eliminated by one "genetic death."

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Figures

Figure 1

Figure 1

Relative frequency of affected children of normal parents (ordinate) as a function of paternal age (abscissa). (Left) Apert syndrome, n = 111. (Center) Achondroplasia, n = 152. (Right) Neurofibromatosis, n = 243. From ref. .

Figure 2

Figure 2

Truncation selection. All of the individuals to the right of the truncation point (those in the shaded area) are eliminated by pre-reproductive death or failure to reproduce. In this example, 10% are eliminated and 90% contribute to the next generation. From left to right, the numbers along the abscissa are the mean number of mutations per individual in the selected group, in the population before selection, at the truncation point, and in the group eliminated by selection.

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