60 



PHYSICAL BASIS OF HEREDITY 



If at the maturation (whether of egg or sperm) taU and 

 color go to one cell, then short and white go to the other 

 cell; but if one of the pairs is turned, so to speak, the 

 other way, thus 



short color 



tall white 



so that short and color go to one cell, then taE and white 

 go to the other. Four classes of germ-cells are expected 

 in Fi, namely, 



tall color, tall white, short color, short white. 



Chance meeting of any one of these four kinds of pollen 

 grains with any one of the same four kinds of eggs will 

 give the sixteen recombination classes shown in the fol- 

 lowing table: 



tall color 



tall white 



short color short white 



Sperm 

 tall color 



tall white 

 short color 

 short white 



The four kinds of eggs are written above and the four 

 kinds of sperm are written to the left. There are 16 pos- 

 sible combinations. Since tall and color are dominant 

 the recombinations give : 9 tall color, 3 tall white, 3 short 

 color, 1 short white. In this table the genes have the 

 same name as the character for which they stand, and 

 these names are written out in full, but it is generally 

 more convenient to use symbols for the genes in order 



