436 



SCIENCE PROGRESS 



it, it is a case of a union between a Y R egg-cell and a Y W 

 pollen-cell ; the result is a Y R zygote, which is a homozygote 

 regards colour and a heterozygote as regards shape. In the 

 next square to the right a Y R gamete meets a G R gamete ; 

 the result is again a Y R zygote, which differs from the last in 

 that it is homozygote as regards shape and heterozygote as 

 regards colour. In the last square on the top line a Y R gamete 

 meets a G W one ; the result is a Y R which differs from any 

 of the preceding ones by being heterozygote both as regards 



YR 



YW 



9£ 



?w 



Yd YW $R §w 



YR 



YR 



YR 



YR 



YR 



YW 



YR 



YW 



YK 



l^x^. 7 



YR 





GR 



YR 



YW 



GR 



QW 



colour and shape. And so on throughout the table. The 

 nature of the sixteen possible kinds of unions of gametes is 

 written in small letters in the sixteen squares of the table. 

 The characters of the resulting zygotes are written in large 

 letters. When this explanation is being illustrated with 

 counters, the nature of the zygote in each case is given by 

 making it a rule always to put a yellow on the top of a green 

 counter and a red on the top of a white. 



The result therefore of allowing our Y R hybrid (produced 

 by Y W and G R) to self-fertilise should be : 



9 Yellow round (squares i, 2, 3, 4, 5, 7, 9, 10, and 13). 

 3 Yellow wrinkled (squares 6, 8, and 14). 



