HYBRIDS, SEGREGATION 



387 



applicable where the heterozygote is intermediate between the 

 two parents, or, as in some cases, even differs from both. 

 A hybrid intermediate between the two parents is obtained, 

 for instance, when the Star and Chinese Primroses are 



RB. 



Rl/. aB. air. 



al-. 



FIG. 225. Scheme to illustrate the progeny of the second generation 

 when two pairs of characters (A a, Bb) are taken into consideration. 

 The individuals of the first generation will all have the constitution 

 AaBb. When segregation occurs, the resulting gametes will have 

 the four possible constitutions AB, Ab, aB, ab, 1 and the scheme shows 

 the possible methods of combination of such gametes. When both 

 dominants are present (in nine out of the sixteen cases) the squares 

 are cross-hatched, when the dominant A is present the shading slopes 

 from left to right, when B is present from right to left ; when neither 

 dominant occurs the square is left unshaded. 



crossed. The petals in the first generation are intermediate in 

 character between those of the two parents (Fig. 226) ; in the 

 second generation segregation takes place in the usual way, 

 the hybrid-individuals (one-half) still exhibiting flowers of the 



1 The combinations A a and Bb do not arise, since dominant and reces- 

 sive characters are segregated. 



