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XXII 



INTRODUCTION TO THE 

 GENETICS OF MAN AND THE FRUIT 

 FLY; REGENERATION OF PLANARIA 



(Readings: C. M. Williams, "The Metamorphosis of Insects," Sci. Am. 182, 

 No. 4, 24-28, April 1950, Reprint No. 49. Weisz, Chapter 27. S.P.T., pp. 159- 

 161; 240. Villee, pp. 496-508. R. Buchsbaum, Animals Without Backbones, 

 Univ. of Chicago Press, rev. ed., 1948, Chapters 10 and 12.) 



In this laboratory section, beyond considering 

 a few simple examples of human genetics, we 

 will begin a four-week program of genetics ex- 

 periments on the fruit fly, Drosophila. While 

 these experiments develop, we shall have ample 

 time to do other things. During the present 

 period you will begin experimenting with the 

 regeneration of a planarian. There will also be 

 slides on display demonstrating meiosis and 

 mitosis in a variety of animals and plants; and 

 also stained preparations of the giant chromo- 

 somes of the salivary glands of Drosophila 

 larvae. 



ASPECTS OF HUMAN GENETICS 

 PTC tasting 



The substance phenlythiocarbamide (PTC; 

 phenylthiourea) tastes very bitter to some per- 

 sons ("tasters") but is tasteless to others ("non- 



tasters"). The abiUty to taste it is inherited as a 

 dominant characteristic. About 70% of the 

 American population taste PTC, the other 30%, 

 who are homozygous for the recessive allele, do 

 not taste it. 



Pieces of paper which have been impregnated 

 with PTC will be provided. Hold a piece in your 

 mouth for about 30 seconds to determine 

 whether or not you are a taster. How does the 

 class come out as a whole? 



Excretion of methyl mercaptan 



Asparagus contains the organic sulfur com- 

 pound dimethylthetin ((CH3)2S"^-CH2COOH). 

 About 60% of the American population possess 

 an enzyme which catalyzes the conversion of 

 dimethylthetin to methyl mercaptan (CH3SH). 

 It is the latter substance that gives urine its 

 characteristic odor after asparagus is eaten. The 

 presence of the enzyme is a dominant trait. 



114 



