INDEPENDENT MENDELIAN INHERITANCE 



85 



purple grains were obtained, but further breeding tests showed that 

 these were simply heterozygous for purple coloration. A real exception 

 must, however, be made for certain families which showed aleurone 

 color segregation in the ratio 9 purple:? white. Such results depend 

 on the presence of two color factor differences and they will be explained 

 later. The results in F 2 and F 3 for these plants of the genetic consti- 

 tution WwSs are tabulated in Table XI. The expected results in each case 

 are given in italics. 



Throughout the results in this table are substantially in agreement 

 with theoretical requirements. The hypothesis has, however, been sub- 

 jected to the further test of growing F 3 populations. Table XII shows the 

 kind of F 3 populations which are to be expected when F^ grains from 

 this cross are planted. All these types of populations were secured. The 

 case, therefore,- provides an excellent illustration of the way in which a 

 Mendelian experiment is carried out and of the excellent agreement 

 with theory which is given in such experiments. 



TABLE XII. F 3 RATIOS TO BE EXPECTED FROM THE DIFFERENT GENOTYPES IN THE 



CROSS WWss X wwSS 



In the animal kingdom important work has been done in establishing 

 Mendelian principles by the use of small animals, particularly mice, 

 rats, guinea-pigs and rabbits. Such animals are particularly favorable 

 for investigations in heredity because a large number of generations may 

 be reared in a relatively short space of time. Castle has reported an 

 excellent case of dihybridism in the guinea-pig. Rough coat is dominant 

 to smooth and colored coat to the albino condition. When a smooth 

 black is crossed with rough white the hybrids are rough black. In F 2 



