MENDEL'S LIFE AND WORK 25 



giving a ratio of almost exactly 3 dominant to 1 

 recessive in every case. When two or more pairs 

 of characters were present in the same cross the 

 results were exactly the same for each pair of 

 characters, bnt the characters themselves were 

 associated in every possible way and not merely 

 as in the parent plants, while the ratios for the 

 different types of combination ai)proximated with 

 great accuracy to a multiplication of the 3 : 1 ratio 

 by itself as many times as there Avere additional 

 pairs of characters associated with the first pair. 

 Thus when two pairs of characters were associated 

 in the cross, four types of plants w^ere produced in 

 the following proportions : — 9 : 3 : 3 : 1, which is 

 evidently the result of 3 + 1 x 3 + 1. Some 

 actual figures obtained by Mendel in the case of 

 crosses between round yellow and wrinkled green 

 seeded forms were : — 



315 RY : 101 WY : 108 RG : 32 W^ G. 



If Mendel had stopped at this point in his 

 investigation it is very unlikely that he would have 

 been led to his great discovery. But by continuing 

 his work into the next and still later generations 

 he was able to show that the apparently simple 

 ratio of 3 : 1 for each pair of characters was really 

 a ratio of 1:2:1, for whereas the one recessive 

 in every four individuals was pure for its character, 

 of the other three, i.^.,the dominants, only one Avas 

 found to breed true, the other two proving to be 

 hybrids exactly the same as their hybrid parents, and 



