SEGREGATION AND DOMINANCE 127 



MALE GAMETES 



T i 



That is, one out of four possible cases was dwarf, t, 

 in character and the other three were apparently 

 tall, although only one out of the three was pure tall, 

 T, while the remaining two were tall with the dwarf 

 character latent, T (t). 



The same thing may be expressed more graphically 

 by the checkerboard plan, 

 which Punnett suggested 

 (Fig. 42). Each square 

 of the checkerboard rep- 

 resents a zygote which, 

 having received a gamete 

 from each of the two par- 

 ents, may develop into a 

 possible offspring. The 

 character of the gametes 

 of the parents is shown 

 outside of these squares, 

 while the arrows repre- 

 sent the parental source 



from which the offspring have received their heredi- 

 tary composition. 



The essential feature of Mendel's law is briefly 

 this: hereditary characters are usually independent 

 units which segregate out upon crossing, regardless of 

 temporary dominance. 



Mendel carried on further experiments with garden 

 peas, using other characters. He obtained practically 

 the same result as in the instance already given, for 

 the actual progeny in the second generation of the 

 cross-bred offspring figured up, as seen in the table 



FIG. 42. Diagram to illustrate 

 theoretically the formation of the 

 four possible zygotes in the second 

 filial generation of a monohybrid. 



