Sex Determination (/) 99 



13.3. Is it possible to consider the factors responsible for the meiotic process separately 

 from the factors responsible for gamete formation? Explain. 



13.4. Why is meiosis the feature most fundamental for the success of sexuality? 



13.5. Do you think the evidence presented is conclusive that sex in Chlamydomonas is 

 based primarily upon a single pair of genes? Justify your answer. 



13.6. Write the genotypes and phenotypes of the unexceptional, nondisjunctional, and 

 gynandromorphic offspring from a mating of P^'/f X jf Drosophila. 



13.7. Are there isoalleles for the genes determining the size and shape of the bristles and 

 hairs of DrosophilcP. Explain. 



13.8. Using first the autosomal alleles e and e+ and then the X-linked alleles y and 7+, 

 design crosses by which you could identify gynanders in Drosophila resulting from 

 two fertilizations of a single egg. 



13.9. Compare the genotypes and phenotypes of gynanders of flies, moths, and men. 



13.10. "All human beings have the same number of chromosomes in each somatic cell." 

 Discuss this statement, giving evidence in support of your view. 



13.11. The following types of mosaics are known in human beings: 



XXX/XO XXY/XX 



XX/XO XXXY/XY 



XY/XO 



Explain how each of these could have originated. 



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

 sexes? Explain. 



