by the National Council on Radiation Protection and Measurements (NCRP). The title of his lecture, "How Well Can We Assess Genetic Risks? Not Very," suggests his theme. Crow summarizes succinctly the evidence linking radiation exposure and the induction of deleterious mutations, and discusses the important concept that the useful variability in our species derives "from the segregation and recombination of existing genes, not from new mutations" (p. 12). Crow suggests that any attempts we may make at risk estimation should focus on (1) cytogenetic changes and (2) clinically severe gene mutations, since the long-range effect of minor mutants, which may represent a significant proportion of all induced mutations, is difficult, if not impossible (and perhaps unnecessary), to estimate, depending, as they do, for their expression on the environment of the time.
In an attempt to demonstrate the impact of an altered mutation rate, Crow cites the work of H.J. Muller and J.B.S. Haldane, in which "the effect of a mutant is measured in terms of its effect on fitness" (p. 23), with the impact of the mutants then being determined by their frequency and not by their clinical severity. Crow concludes his lecture by noting that our best bet in estimating risks lies in assessing the short-term risks (as by studying traits with a high half-sib correlation) rather than the long-term cumulative risks, which, in terms of magnitude, are likely to be very small in future generations.
This lecture is interesting reading for those concerned about the genetic future of our species, especially with respect to induced mutations and their consequences, be those mutations induced by ionizing radiations or other environmental agents.