238 CHAPTER 27 



QUESTIONS FOR DISCUSSION 



27.1. In each of the following cases, explain whether the rate with which a particular allele 

 mutates is of primary importance in shifting its frequency in the population, when 

 this gene: 



a. is a dominant lethal in early developmental stages. 



b. is a recessive lethal. 



c. expresses itself phenotypically only after the repro- 

 ductive period of the individual. 



d. is very rare. 



e. occurs in small cross-fertilizing populations. 



27.2. Can the adaptive value of the same gene differ: 



a. in haploids and diploids? 



b. in males and females? 



c. in two diploid cells of the same organism? 



Explain your decision in each case. 



27.3. Other things being equal, what would happen to the frequency in the gene pool, of 

 a dominant mutant whose selection coefficient changed from 1 to '4? What would 

 happen in this respect if the mutant was completely recessive? 



27.4. If persons carrying detrimental mutants fail to marry, these particular genes are re- 

 moved from the gene pool. Under what conditions is the failure to marry likely 

 to reduce appreciably the frequency of detrimental mutants in the gene pool? 



27.5. Are inbreeding and assertive mating mutually exclusive departures from random 

 mating {panmixis)! Explain. 



27.6. Explain why the inbreeding coefficient, F, is Ke for cousin marriages. 



27.7. Suppose the frequencies of A and a are .3 and .7, respectively, in a population obeying 

 the Hardy-Weinberg rule and in which mating is at random. 



a. What per cent of the population is composed of homozygotes with respect to 

 these genes? 



b. What would be your answer to a. after one generation in which hybrids could 

 mate only with hybrids? 



c. What effect would the conditions in b. have upon the composition of the gene 

 pool? 



27.8. Discuss, from a genetic standpoint, the advantages and disadvantages of cousin 

 marriages in man. 



27.9. In Thailand, heterozygotes for a mutant gene that results in the formation of hemo- 

 globin E are more frequent in the population than would be expected if the Hardy- 

 Weinberg equilibrium obtained. How can you explain this? 



