GENETICS 243 



41. The character known as speck (s), a spot near the base of the wing in Dro- 

 sophila, is recessive to no speck (S), and plexus (p), a tangled patch of wing veins, is 

 recessive to no plexus (P). A doubly heterozygous no-plexus no-speck female (PpSs) 

 is mated with a plexus speck male (ppss). Of their 200 offspring, 10 are plexus 

 no-speck. How do you account for the smallness of this number? How many of the 

 offspring should be plexus speck? 



42. In four-o'clocks the red flower color is not wholly dominant over white, so that 

 heterozygous flowers (Pr) are pink. What would be the appearance of the offspring 

 of a self-fertilized pink-flowered plant? If the progeny of this plant numbered 100, 

 how many red ones should there be? 



43. If a pink-flowered four-o'clock is pollinated from a red one, and they produce 

 84 offspring, how many of these should be red? 



44. In shorthorn cattle, the hybrid between red and white is roan (having white 

 hairs and red hairs intermingled). What would be the nature of the offspring of a 

 roan and a white animal? The offspring of a roan and a red animal? 



46. In Drosophila, cinnabar eye is recessive to red, stripe (a mark down the back) 

 is recessive to no stripe, and bent wing recessive to straight wing. A cinnabar stripe 

 bent fly is mated with a homozygous red no-stripe straight (wild-type) fly, and their 

 offspring crossed with cinnabar stripe bent flies. Of 288 offspring from this latter 

 cross, how many should be red stripe straight? 



46. If two Fi flies from Problem 45 are mated together, and among their r2 off- 

 spring there are 36 cinnabar no-stripe straight-winged individuals, how many wild- 

 type flies would be expected in the F2 generation? How many red stripe bent flies? 



References 



Bateson, W. Mendel's Principles of Heredity. Cambridge University Press. 



(Part II: biography of Mendel, translations of his papers.) 

 Shull, a. F. Heredity. 3d Ed. McGraw-Hill Book Company, Inc. (Chaps. 



VII-XIII on simple heredity; rest of book deals with more complex inheritance 



and emphasizes applications to human affairs.) 

 SiNNOTT, E. W., and L. C. Dunn. Principles of Genetics. 3d Ed. McGraw-Hill 



Book Company, Inc. (Chaps. Ill and IV for Mendel's laws.) 



.^^. 



