PEDIATRICS Vol. 53 No. 5 May 1974, pp. 800-807
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Monitoring for Human Mutagenesis

H. Eldon Sutton 1

1 Department of Zoology, University of Texas at Austin

Mutation is an intrinsic property of genes and has provided the variability that we value as a characteristic of human populations as well as the variability that was necessary for evolution to occur. Nevertheless, an increase in mutation rate is almost universally regarded as undesirable. The likelihood that a random change in a gene will be beneficial to the host is small. The likelihood that it will be detrimental is much larger. There is much argument as to the proportion of genes that truly are neutral, but these are of no special concern to the present discussion.

When a detrimental mutation occurs, it is expressed ultimately as failure of a zygote to develop, as abortion, as overt disease, or as reduced fertility. The expression may be immediate or delayed, depending on the degree of dominance of the mutalion. The social consequences of these different outcomes are different, much more so than the genetic consequences. A genetic death is failure to survive and reproduce, whether that failure be due to early death (as in Tay-Sachs disease) or to reduced fertility in an otherwise healthy person.

Such detrimental genes are removed eventually from the population through natural selection—rapidly if the mutant allele is expressed in the heterozygote, much more slowly if the allele is completely recessive. Eventually an equilibrium is reached, with the number of mutant alleles eliminated by selection equal to the number produced by mutation. In the case of recessive alleles, many generations are required to establish a new equilibrium.