INVESTIGATIONS SINCE MENDEL 553 



the absence of the extra factors for size. If the tall variety is 

 32 inches taller than the small variety, each of the factors A , B, 

 C, and D represents 4 inches in height. Now the gametes of 

 the tall variety have A BCD in them, while the corresponding 

 constitution of the gametes of the small variety is abed, and 

 the fertilized eggs and first generation of hybrids resulting 

 from the cross between these two varieties have the formula 

 AaBhCcDd. Now since each factor for height represented by 

 the large letters is responsible for 4 inches of height, the individ- 

 uals of the first generation of hybrids should be 16 inches taller 

 than the small variety but 16 inches shorter than the tall variety. 

 They are intermediate in height between the two parents. The 

 hybrids form gametes having the constitution ABCD, aBCD, 

 abCD, abcD, abed, AbCD and so on, involving all the combina- 

 tions that can be made with the four pairs of letters. In fertili- 

 zation all possible combinations of the various kinds of gametes 

 can take place, and consequently individuals of eight various 

 sizes can occur in the second generation of hybrids. Thus, if a 

 gamete with a constitution abed unites with a gamete with the 

 constitution abcD, the resulting offspring has the constitution 

 aabbeedD and should be 4 inches higher than the smaller variety 

 of the parent generation. If a gamete with the constitution 

 ABCD unites with a gamete having the constitution abCD, the 

 resulting offspring, which has the factors aAbBCCDD, should 

 be 24 inches higher than the smaller variety or 8 inches lower 

 than the taller variety of the parent generations. It is, there- 

 fore, obvious that due to the various kinds of combinations 

 that may occur among the gametes, individuals of various 

 sizes may occur in the second hybrid generation. 



Another peculiar situation which has been discovered among 

 both plants and animals may be illustrated by the behavior of 

 color in the Andalusian fowl. These fowls are what fanciers 

 call blue, but when they are bred together the offspring con- 

 sist of black, blue, and white fowls, and the proportion is accord- 

 ing to the Mendehan ratio 1 : 2 : 1. The black and white fowls 

 breed true, but the blues breed as before. When black and 

 white fowls are crossed, blue fowls are obtained. The blue is 

 therefore a result of a heterozygous condition in which the 

 factor for black is combined with a factor for white. In this 

 case the hybrids may be regarded as having a different character 



