50 



INTROGRESSIVE HYBRIDIZATION 



hbdd is completely glabrous, and BbDd is exactly interme- 

 diate. 



What we shall now consider is the way in which the cross 

 between a strongly obovate, heavily pubescent AABBCCDD 



AACC 4 



aacc 



^^BBDD 



Fig. 9. A hypothetical example of multiple factor differences affecting 

 two characters, leaf shape and pubescence. Genes B and D vs. b and d 

 are supposed to have equal effects upon pubescence and none upon leaf 

 shape. Genes A and C vs. a and c are supposed to have equal effects 

 upon leaf shape and none upon pubescence. The frequencies of Figs. 

 10 to 17 all refer to this figure. The predominating leaf types in the 

 "spindle of recombination" are slightly darker than the other types. 



and a strongly ovate, completely glabrous aabbccdd will be 

 affected by linkage. We are assuming that there is no dom- 

 inance and no complicated gene interactions and that all 

 4 genes affecting each character have simple, additive ef- 



