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COLLEGE ZOOLOGY 



developing organisms are subjected to radia- 

 tion, some of the genes in certain individuals 

 become changed; these modified genes are 

 inherited like normal genes and give rise to 

 changes in the traits of the individual bear- 

 ing them. Such gene mutations, as a result 

 of radiation, have been described in both 

 plants and animals. Besides single gene 

 mutations, there are those which involve 

 chromosome changes. An example is dele- 

 tion, where a piece of a chromosome is lost. 

 Ultraviolet light has produced both gene 

 and chromosome mutations. Some other 

 agents inducing mutations are: cosmic rays, 

 high temperature, formaldehyde, mustard 

 gas, and hydrogen peroxide. Of special im- 

 portance is the fact that certain cancer-in- 

 ducing chemicals also produce mutations. 



Radiation genetics 



Radiation genetics is the study of the 

 effects of radiation on heredity. 



Radiation 



Of greatest present interest is the fact 

 that radiation is known to increase muta- 

 tions. Doubtless mutations have been pro- 

 duced among the Japanese by the effect of 

 the atomic bombing in Japan in World 

 War II. Muller has said, "I do not think 

 that geneticists would question that reces- 

 sive mutations so produced will go down 

 for hundreds of generations." Geneticists 

 seem agreed that an increase of mutation 

 rates in human populations will add to the 

 store of human miser)\ This is why there is 

 world-wide concern about the genetic effect 

 of any kind of increased radiation. 



Fallout 



A nuclear explosion emits great amounts 

 of radiation, and even "small" explosions 

 send appreciable amounts of material into 

 the upper atmosphere. Here the prevailing 

 winds cause the radioactive particles to move 

 eastward and around the world in four to 

 seven weeks. 



Fallout affects human beings either di- 

 rectly through increasing external penetrat- 

 ing radiations, or indirectly by contaminat- 

 ing the food they eat or the air they breathe. 

 Fallout is widely distributed over the whole 

 globe, and everjone encounters some of its 

 radioactive particles. However, the Atomic 

 Energy Commission recently estimated the 

 external dose from fallout to date to be 

 from 0.001 to 0.005 roentgens per year. The 

 latter figure is only a 5 per cent increase 

 over the natural radiations we already re- 

 ceive. Moreover, it has been estimated that 

 we receive about as much radiation from 

 medical and dental X-rays as we do from 

 natural sources. Hence any body (somatic) 

 or genetic damage produced by fallout must 

 be only a small fraction of that which is 

 already being produced by natural and artifi- 

 cial radiations. Whether one considers a 

 small increase in human suffering and death 

 negligible depends on whether one is con- 

 sidering the question from the individual's 

 or the population's point of view. Consider- 

 ing present radiation levels from both points 

 of view, geneticists have reached the con- 

 sensus of opinion that we must limit, as 

 much as possible, exposures to fallout and 

 other radiation sources under human con- 

 trol. 



How do genes act? 



An increasing number of investigations 

 are concerned with the role of the gene in 

 controlling development and the role of the 

 gene in the synthesis of new substances. 

 One organism much used in gene-action in- 

 vestigations is a bread mold, Neurospora, 

 which has been found convenient for both 

 genetic and biochemical studies. As found 

 in nature, this bread mold is capable of 

 synthesizing all its cell constituents from 

 water, sugar, inorganic nitrogen, certain in- 

 organic salts, and the vitamin known as 

 biotin. By exposing the mold to X-rays, it 

 has been possible to obtain mutant types 



