MENDEL'S SECOND LAW 



63 



example, the normal, meaning the wild type in each factor 

 pair, is represented by N, the foregoing table becomes : 



Eggs 



Sperm 



NN 



Nw 

 sN 

 sw 



NN 



Nw 



bN 



In the preceding illustration one grand-parent (Pi) was 

 assumed to have had both dominant characters (tall and 

 colored), while the other grand-parent had both reces- 

 sives (short and white). Obviously the grand-parents 

 might have happened to be made up differently — one 

 might have been tall and white, the other short and col- 

 ored. The Fi plants (Ss, Ww) would have been the 

 same in either case, and so would the F2 results. In 

 other words, for the principle of assortment it should 

 make no difference from which parent the characters have 

 come. This is illustrated in the following cross (Fig. 29), 

 in which a wingless vestigial (recessive) Drosophila 

 male having the wild- type color (dominant) is bred to 

 long-winged (dominant) female with ebony (recessive) 

 body color. The F^ flies have long wings and wild type 

 body color. Inbred, they give 9 long wild type color, 3 

 long ebony, 3 vestigial wild type color, and 1 vestigial 

 ebony. In the diagram the gene for vestigial is repre- 

 sented by V, and its allelomorph for long wings by V; the 

 gene for ebony by e, its allelomorph for wild type color 

 by E. The germ-cells of the two Pi flies are therefore 

 vE and Ve. Each contains the wild-type allelomorph 

 of the recessive mutant gene in the other parent. The 



