-It CHAPTER 15 



15.3. Discuss the statement: "The Hardy-Weinberg Law is the cornerstone of evolu- 

 tionary genetics." 



15.4. Assuming that the Hard) Weinberg principle applies, what is the frequency 

 o\ the gene R h us onlj allele R' is homozygous in the following percentages 

 of the population: 49%? 49? ? 25%? 36%? 



15.5. In the United Stales about 709? of the population gets a hitter taste from the 

 drug phenyl thiocarbamide (PTC). I hese people are called "tasters" and the 

 remaining 309? who get no hitter taste from PTC are called "nontasters." All 

 marriages between nontasters produce all nontaster offspring. Every experi- 

 mental result supports the view that: a single pair of nonsex-linked genes de- 

 termines the difference between tasters and nontasters; dominance is complete 

 between the only two kinds of alleles that occur; penetrance o\ the dominant 

 allele is complete. 



( a ) Which of the two alleles is the dominant one? 



(b) What proportion of all marriages hetween tasters and nontasters have no 

 chance (barring mutation) of producing a nontaster child? 



(c) What proportion of all marriages occurs between two nontasters? Two 

 tasters? 



15.6. The proportion of A A individuals in a large crossbreeding population is .09. 

 Assuming all genotypes with respect to this locus have the same reproductive 

 potential, what proportion of the population should be heterozygous for A) 



15.7. What do you suppose would happen to a population whose gene pool obeyed 

 the Hardy-Weinberg rule for a very large number of generations? Why? 



15.8. Can a population obey the Hardy-Weinberg rule for one gene pair but not 

 for another? Explain. 



15.9. Explain whether the mutation frequency to a particular allele is of primary im- 

 portance in shifting its frequency in the population, when this gene is: 



(a) a dominant lethal in early developmental stages 



(b) a recessive lethal 



(c) phenotypically expressed only after the reproductive period of the individual 



(d) very rare 



(e) present in small cross-fertilizing populations 



15.10. Can the adaptive value of the same gene (15.9) differ in: 



(a) haploids and diploids? 



(b) males and females? 



(c) two diploid cells of the same organism? 



Explain your answer in each case. 



15.1 1. Other things being equal, what will happen to the frequency in the gene pool of 

 a dominant mutant whose selection coefficient changes from one to V? If the 

 mutant is completely recessive? 



15.12. If persons carrying detrimental mutants never marry, these particular genes are 

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

 likely to appreciably reduce the frequency of detrimental mutants in the gene 

 pool? 



15.13. Are inbreeding and assortive mating mutually exclusive departures from random 

 mating (panmixis)? Explain. 



15.14. Explain why the inbreeding coefficient, F, is Vie for cousin marriages. 



