Ill ( HAPTER 8 



S.S. Compare the genotypes and phenotypes of sex chromosome mosaics of flies, 

 mollis, and men. 



8.9. All human beings have the same number o\ chromosomes in each somatic cell. 

 Discuss this statement giving evidence in support of your view. 



8.10. The following types oi mosaics are known in human beings: 



XXX/XO XXY/XX 



XX/XO XXXY/XY 



XY/XO 



Give a reasonable explanation lor the probable origination of each. 



8.11. In human beings, can the members of a pair of monozygotic twins ever be of 

 different sexes? Explain. 



S.I 2. Does a gene have to have an alternative allele before it can be discovered? 

 Explain. 



8.13. Assuming each homolog carried a different allele, a 1 , a 2 , a'\ o\ the same gene, 

 make a schematic representation of a trivalent as it might appear during synapsis. 

 Show diagrammatically the chromosomal and genetic content of the four meiotic 

 products that could be obtained from your trivalent diagram. 



5.14. Ignoring chiasma formation, how many chromosomally-different kinds of eggs 

 can a triploid Drosophila female produce? How many of these eggs have more 

 than a 5% chance of occurring? 



8.15. (a) Scurfy, sf, is an X-linked recessive gene that kills male mice before they repro- 

 duce. How is a stock containing this gene maintained normally? 



(b) Occasionally, the stock containing this gene produces scurfy females which 

 also die before reproductive age. Suggest a genetic explanation for these female 

 exceptions. Describe how you would test your hypothesis genetically by trans- 

 planting ovaries and obtaining progeny from them. 



8.16. What explanations can you offer, other than those already presented, for the 

 shift in sex ratio with age of human parents? 



8.17. No Y0 human beings are known. Why is this chromosomal constitution con- 

 sidered to be lethal? 



8.18. List the types of human zygotes formed after maternal nondisjunction of the 

 X chromosome. What phenotypes would be expected for each of the zygotes 

 that these, in turn, may produce? 



8.19. List specific causes for the production of abnormal sex types in human beings. 



8.20. How can you explain that only one X0 individual is known to have had a suc- 

 cessful pregnancy, whereas other XO's are sterile? 



8.21. Discuss the general applicability of the chromosomal balance theory of sex 

 determination. 



8.22. In Drosophila, why are gynanders not intersexes? Is this true in man also? 

 Explain. 



8.23. What chromosomal constitution can you give for a triploid human embryo that 

 is "male"? ■"Female"? 



8.24. A non-hemophilic man and woman have a hemophilic son with Klinefelter's 

 syndrome. Describe the chromosomal content and genotypes of all three indi- 

 viduals mentioned. 



