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QUESTIONS FOR DISCUSSION 



39.1. If essentially all of one X chromosome in a human female is functionally turned 

 off in somatic tissues, what is the disadvantage of having 9 = X and 6 = X Y? 



39.2. Almost without exception, piebald or tortoise-shell cats are females. Explain. 



39.3. What kind of autosomal genes would be unsuitable for the experiments with mice 

 described on p. 486? 



39.4. Discuss the phenotypes expected among females heterozygous for the X-linked 

 mutant for hemophilia. 



39.5. Compare the dosage compensation mechanism in mice with that in Drosophila. 



39.6. How can studies of twins test the hypothesis of dosage compensation? 



39.7. What explanations can you give for the occurrence of females heterozygous for 

 the X-linked mutant for red-green colorblindness but who are colorblind only 

 in one eye or in portions of one eye? For identical female twins, one colorblind 

 and one not colorblind? 



39.8. Ocular albinism is an X-linked mutant that causes the retina of human males 

 to be colorless. What phenotype would you expect in heterozygous females if 

 the mutant is 



(a) Completely recessi\c' 



(b) Completely dominant? 



(c) Partially dominant? 



Such females actually contain patches of both albino and normally pigmented 

 retina. What bearing does this finding have upon questions (a), (b). (c) above 

 and to vour answers? 



