i8a MENDELISM 



breeding. Tiiis conclusion is at least so far firmly 

 established that no alternative hypothesis has been 

 put forward which will explain the facts. 



We have next to consider what will be the result of 

 crossing our cross-bred plants with one another instead 

 of with the pure white form. The following possi- 

 bilities present themselves : 



A yellow female gamete may pair with a yellow male gamete. 



, white 



A white yellow 



r> n white 



All these combinations are equally likely to occur, 

 because in each plant there are the same number of 

 yellow and white female gametes as well as of yellow 

 and white male gametes. In the long-run, therefore, 

 each of the above pairings will be found to have taken 

 place in an equal number of cases. The grains which 

 we shall obtain, then, will be yellow and white in colour, 

 and the two kinds will occur in the following propor- 

 tions : i pure white ; 2 white x yellow or yellow x 

 white, which, as we have already seen, will be yellow 

 in appearance ; and i pure yellow. Altogether, we 

 shall expect a ratio of 3 yeDow grains to i white. 



In an actual experiment the following result was 

 obtained : 



Yellow grains 16,592, or 74*5 per cent. 



White 5,681, 25-5 



that is to say, a ratio of 2-9 yellow to i white. 



The expression lA \2Aai la, in which A represents 

 the dominant character (yellow) and a the recessive 

 character (white), may be spoken of as a Mendelian 



