Regulation of Gene Action — Dosage Compensation 491 



39.9. An X-linked mutant in the human male prevents perspiration in any part of 

 the body. What do you suppose would happen to a heterozygote for this mutant 

 who dusted her body with a dry mixture of starch and iodine and then entered 

 a hothouse? 



39.10. How can you account for the fact that X0, XX, and XXX women (or XY and 

 XXY men) are not phenotypically equivalent? Does your answer hold true 

 for the female mouse (the X0 is usually fertile)? 



39.11. What do you think of the hypothesis that dosage compensation in mammals 

 starts because one chromosome (or part of one) is precociously used as tem- 

 plate? 



39.12. What can you conclude from the observation that in human females heterozygous 

 for an abnormal X — the mutant X being either rod shaped but shorter or longer 

 than normal, or ring shaped — the abnormal X appears in Barr bodies more fre- 

 quently than the normal X homolog? 



39.13. Discuss the significance of work with the toad Xenopus (discussed on p. 427) 

 relative to dosage compensation. 



