PROBLEM 2. Differences Between Parents and Offspring 



471 



Fu;. 420 Half-pint milk bot- 

 tles make cheap homes for 

 faiiiilies of fruit flies. In a 

 laboratory ivhere fruit flies 

 are studied., you would see 

 row after row of such bot- 

 tles. Each contains flies with 

 some character or group of 

 characters to be followed in 

 experiments, (professor h. 

 charipper) 



We can explain Mendel's results in 

 crossing pea plants that were pure for 

 tallness and for yellow seeds with pea 

 plants that were pure for shortness and 

 for green seeds. If you ^vill examine 

 Figure 421 you will note that all the F^ 

 plants were tall and bore yellow seeds. 



Pi 



Fi 



TT YY 



X 



All gametes [TY 



Ts Yg 



(tall yellow) 



Fig. 421 What characters does each parent 

 have? Is each parent pure or hybrid for size? 

 For seed color? Is the (F^) pure or hybrid for 

 size? For seed color? How does it look? 



Mendel then mated to each other the F^ 

 plants which were hybrid for both size 

 and seed color. Four kinds of plants re- 

 sulted. Some w^ere tall with yellow seeds, 

 some tall with green seeds, some short 

 with yellow seeds, and some short with 

 green seeds. 



(Optional) Independent assortment. 

 Since we understand reduction division, 

 we can see the reason for the results. The 

 genes for size are located in one pair of 

 chromosomes and the genes for seed 

 color are in a different pair. Because of 

 this there are four possible kinds of gam- 

 etes when the primary sex cells of the 



(all have the same 

 make-up no matter 

 how many offspring) 



Fig. 422 Heredity of fruit flies with long and 

 with short {vestigial) wings. Which character 

 is dominant? How do you know? In what ratio 

 will long and vestigial wings appear in the F^ 

 if large numbers of flies are produced? 



