CHARACTERS OF DISTINCT PAIRS 97 



prefixed to them. This proportion is a very impor- 

 tant one ; it is, therefore, desirable to make this 

 point perfectly clear. In the second hybrid genera- 

 tion resulting from a cross between a yellow wrinkled 

 and a green round pea there will be : 



9 Yellow round, 3 Yellow wrinkled, 3 Green round, 

 and 1 Green wrinkled 



in every sixteen peas, on the average. 



It will at once be seen that the peas bearing two 

 dominant characters are in the majority : there are 

 nine out of sixteen. Next come peas with a dominant 

 and a recessive character, which may be either yellow 

 and wrinkled or green and round. Of each of these 

 combinations, there are three in the sixteen. Last 

 of all, in point of number, come those peas both of 

 the characters of which are recessive, namely the 

 green wrinkled ones ; of these there is only one in 

 every sixteen. 



This 9:3:3:1 proportion follows from the 

 co-existence of two 3 : 1 ratios in the second 

 hybrid generation produced by a single cross, in the 

 following way. The two pairs of characters, yellow 

 and green, and round and wrinkled, are distributed in 

 their proportions of three to one, at random, over the 

 individuals composing the second hybrid generation. 

 What is meant by "at random " is that the shape 

 of the cotyledons is not affected, one way or the 

 other, by their colour, or their colour by their shape. 

 It would be an even chance that a round pea were a 

 yellow or green, or that a yellow one were a round 



H 



