Sex Determination (II) 



109 



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

 and many other organisms, a large part of sexual differentiation is under the control of 

 sex hormones produced by the gonads. While this type of control makes the occurrence 

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

 unlikely, it may lead 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 Generics, Peters, J. A. (Ed.), Englewood 

 ClitTs, N.J., Prentice-Hall, 1959, pp. 117-123. 



Goldschmidt, R. B., Theoretical Genet- 

 ics, Berkeley and Los Angeles, 

 University of California Press, 

 1955. 



Shettles, L. B., "Nuclear Morphology 

 of Human Spermatozoa," Na- 

 ture, 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 Droso- 

 pliila Melanogaster that Trans- 

 forms Females into Males," 

 Genetics, 30:297 299, 1945. 



Alfred H. Sturtevant (//; 1945). 



QUESTIONS FOR DISCUSSION 



14.1. Does a gene have to have an alternative allele before it can be discovered? Explain. 



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

 Suppose each carried a different allele, a\ a~, a\ of the same gene. 



Show diagrammatically the chromosomal and genetic content of the four meiotic 

 products you might obtain from the trivalent you drew. 



14.3. 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? 



