Genetic Loads and Their Population Effects 227 



Report of the United Nations Scientific Committee on the Effects of Atomic Radiation, 

 New York: General Assembly Official Records: 13th Session, Suppl. 17 (A/3838), 

 Chaps. 5-6, Annexes G-I, 1958. 



Selected Materials on Radiation Protection Criteria and Standards: Their Basis and Use, 

 Joint Committee on Atomic Energy, Congress of the United States, Washington, 

 D.C.: U.S. Government Printing Office, 1960. 



The Biological Effects of Atomic Radiation, Summary Reports, Washington, D.C.: 

 National Academy of Sciences — National Research Council, 1956 and 1960. (See 

 Reports of the Genetics Committee.) 



Wallace, B., "A Comparison of the Viability Effects of Chromosomes in Heterozygous 

 and Homozygous Condition," Proc. Nat. Acad. Sci., U.S., 49:801-806, 1963. 



QUESTIONS FOR DISCUSSION 



16.1. Do you suppose that the mutations which occur in man serve a useful function? 

 Why? 



16.2. Compare the fate of a mutational load in asexually reproducing populations that 

 are haploid, diploid, and autotetraploid. 



16.3. Discuss the effect upon the gene pool of mutants restricted to the somatic line. 



16.4. Can the gene that comprises part of a detrimental equivalent also comprise part 

 of a lethal equivalent? Explain. 



16.5. Give examples of balanced and unbalanced polymorphism in the genetics of man. 



16.6. What is the relation between phenotypic detriment, genetic death, and genetic 

 persistence? 



16.7. Discuss the relative importance of point mutants and gross structural changes in 

 chromosomes to the individual and to the population. 



16.8. What is the difference, in terms of mutation, between a maximum permissible 

 dose and a doubling dose of ionizing radiation? Is any dose of any radiation 

 safe from a mutational standpoint? Explain. 



16.9. Compare the genetic composition of the mutant load caused by fallout, by med- 

 ical uses of radiation, and by atomic reactor accidents. 



16.10. Do you believe it is essential for the general public to become acquainted with 

 the genetic effects of radiation? Why? 



16.11. What are some of the beneficial uses of radiation? Are any of these based upon 

 the genetic effects of the radiation? If so, give one or more examples. 



16.12. One of the components of fallout is radioactive iodine, 1-131, which has a half- 

 life of about a week. Discuss the genetic effects expected in the somatic and 

 germ lines of persons exposed to fallout. 



16.13. Susceptibility to leprosy may be due to a single irregularly dominant gene. S. G. 

 Spickett notes that leprosy is increasing in some human populations that have 

 been free of it for many generations. List some factors which may be responsible 

 for this finding. 



16.14. Is a genotype adaptive in man today, one which would have been adaptive 2,000 

 or 20,000 years ago? Explain. 



16.15. "The danger of mutation lies primarily in the rate with which it occurs." Crit- 

 icize this statement. 



16.16. How can you explain the finding that in the genus Drosophila apparently the 

 heaviest genetic loads occur in common and in ecologically most versatile species, 

 whereas the lightest loads are found in rare and in specialized species and in 

 marginal colonies of common species? 



