work performed on the fruit fly, drosophila. These data are extrapo- lated to the human situation assuming an increased sensitivity factor of 10, based on mammalian genetic studies with mice. Whereas qualitative- ly man should react in a manner consistent with the fundamental genetic facts as determined by lower forms, the quantitative extrapolation carries more uncertainty. Some of the quantitative concepts so develé oped are: 1. lr =1 lethal mutetion in 1000 germ cells or 1 lethal mutation in 500 conceptions. 2. Detrimental mutations are roughly twice as frequent as lethal mutations. 3. Approximately 44 of recessive lethals will find expression as a genetic death in each generation. h,. The irradiation mutation rate of mature germ cells appears to be about twice the rate of immature germ cells. 5. Detrimental mutations will account eventually for one genetic death per mutation. 6. From statistical considerations it has been estimated that one genetic death will cause elimination of at least two to three mutations. In order to obtain some idea of the genetic effect of fall-out radiation on a population, consider the following situation. Assume: year. 1. Total population of 100 million people. 2. Population is stable and requires 2,700,000 births per For a procreative period of 25 years, this requires 67.5 million births per generation. 3. <A dose of 100 roentgen is delivered to the gonads of each member of the population due to fall-out radiation. =! © 7 If 1 r = 1 lethal mutation in 1000 germ cells or 500 conceptions, for 100 r there will be one lethal mutation in 5 conceptions. Since the generation exposed will produce 67.5 million births, there will be 91