Sex Determination 113 



These principles of sex determination apply also to human beings. In man and 

 many other organisms, a large part of sexual differentiation is controlled by sex hor- 

 mones produced by the gonads. This type of control rarely, if ever, permits the occur- 

 rence of individuals who are typically male in one part and typically female in another 

 part; it may also contribute to the formation of abnormal sex types for nongenetic 

 reasons. 



REFERENCES 



Bangham, A. D., "Electrophoretic Characteristics of Ram and Rabbit Spermatozoa," 

 Proc. Roy. Soc, Ser. B, 155:292-305, 1961. 



Bridges, C. B., "Sex in Relation to Chromosomes and Genes," Amer. Nat., 59:127-137, 

 1925. Reprinted in Classic Papers in Genetics, Peters, J. A. (Ed.), Englewood 

 Cliffs, N.J.: Prentice-Hall, 1959, pp. 117-123. 



Goldschmidt, R. B., Theoretical Genetics, Berkeley and Los Angeles: University of 

 California Press, 1955. 



Hannah-Alava. A.. '"Genetic Mosaics," Scient. Amer., 202:118-130, 1960. 



Lancet, No. 7075, Vol. 1, 1959, pp. 709-716. 



McKusick, V. A., Human Genetics, Englewood Cliffs, N.J.: Prentice-Hall, Inc., 1964. 



Shettles, L. B., "Nuclear Morphology of Human Spermatozoa," Nature, London, 186: 

 648-649, 1960. 



Shettles, L. B., "Nuclear Structure of Human Spermatozoa," Nature, London, 188- 

 918-919, 1960. 



Sturtevant, A. H., "A Gene in Drosophila melanogaster that Transforms Females into 

 Males," Genetics, 30:297-299, 1945. 



Whiting, P. W., "Multiple Alleles in Complementary Sex Determination in Habro- 

 bracon," Genetics, 28:365-382, 1943. 



QUESTIONS FOR DISCUSSION 



8.1. If sexual reproduction is as advantageous as discussed, why do so many organ- 

 isms still reproduce asexually? 



8.2. Does the study of sex determination offer any test of the theory that chromo- 

 somes furnish the physical basis for genes? Explain. 



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

 from the factors responsible for gamete formation? Explain. 



8.4. Why is meiosis the most fundamental feature in the success of sexuality? 



8.5. Give the genotypes and phenotypes of the unexceptional, the nondisjunctional, 

 and the gynandromorphic offspring expected from a mating of f 34b /f with / 

 Drosophila. 



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

 and hairs of Drosophila? Explain. 



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

 devise crosses by which you could identify gynanders in Drosophila resulting 

 from two fertilizations of a single egg. 



