24 



PHYSICAL BASIS OF HEREDITY 



green pods, gray versus white- skinned peas, yellow versus 

 green cotyledons (seen through the skin of the seed), 

 and round versus wrinkled seeds (determined by the 

 nature of the cotyledons mthin the seed coat). 



The 3 : 1, Fo, ratio characteristic for a single pair of 

 characters is the expectation based on the chance meeting 

 of either one of two kinds of eggs with either one of two 

 kinds of pollen grains. In actual numbers this ratio is, 

 of course, not always exactly realized, but only approxi- 

 mately. For the seven pairs of characters that Men- 

 del examined, the Fo ratios were as f oUows : 



Dominants Receesives 



No'a. per 4 



Form of seed 



Color of cotyledons 

 Color of seed coats . 



Form of pod 



Color of pod 



Position of flowers . 

 Length of stem .... 



Totals 



7,324 



8,023 

 929 



1,181 

 580 

 858 



1,064 



5,474 



6,022 



705 



882 

 428 

 651 



787 



1,850 

 2,001 

 224 

 299 

 152 

 207 

 277 



2.99 

 3.00 

 3.04 

 2.99 

 2.95 

 3.03 

 2.92 



1.01 

 1.00 

 0.96 

 1.01 

 1.05 

 0.97 

 1.08 



19,959 



14,949 i 5,010 



2.996 



1.004 



The following collective data for the inheritance of 

 color of the cotyledons of garden peas show that the 

 approximation to a 3 to 1 for the recessive character is 

 very close : 



