Lecture XXIX. 265 



gametes each contributing the alternate determinants, does not 

 possess either allelomorph but has an intermediate character. The 

 classical example of this is furnished by the blue colour of the 

 Andalusian fowl. When blue Andalusian fowl are paired together 

 only half of the chickens produced become blues, the remainder 

 are "wasters," black and dirty whites in about equal proportions. 

 Repeated efforts have been made to breed a pure progeny from 

 blue parents without success. Assuming that the blues are 

 heterozygotes this is what might be expected. This surmise has 

 been established by producing whole progenies of blues without 

 any wasters by pairing the black and white wasters. 



Similar heterozygous forms are produced by plants. Thus the 

 peculiar shade of flower in Primulas known as "crushed straw- 

 berry " cannot exist except as a heterozygous character. It is 

 formed by the united action of the determinants of a pair of 

 allelomorphs, of which one is deep crimson and the other 

 white. 



In the examples just described the inheritance of only one pair 

 of allelomorphs has been considered. When two pairs of allelo- 

 morphs are considered it has been found that the . results are 

 generally explicable on the same hypotheses, namely, that the 

 determinants of opposing allelomorphs are segregated at the 

 formation of the gametes and that the gametes containing these 

 different determinants are formed in equal numbers and unite 

 together indiscriminately. It is further premised that the various 

 determinants are transmitted without influence on, and inde- 

 pendently of, one another. 



Using, for the sake of convenience, the shape and colour allelo- 

 morphs of the peas for our illustration, we will consider the 

 inheritance of these allelomorphs among the descendants of two 

 pure peas, one round and green and the other angular and 

 yellow. 



Here the pairs of allelomorphs are roundness, angularity, and 

 yellowness, greenness. The dominants are roundness and yellow- 

 ness ; angularity and greenness are the recessives. We will de- 

 note the determinants of the two pairs of allelomorphs as R, a 

 and Y, g. 



The gametes of the round and green pea will all contain R and 

 g the determinants of their characters. The gametes of the angular 

 and yellow pea will similarly all contain a and Y. In fertilisation 

 the heterozygote R^aY will be formed. R and Y being dominant 

 this heterozygote will appear round and yellow. 



When this heterozygous embryo grows up, segregation of the 



