Ill MENDEL'S WORK 23 



9 coloured tails, 3 white tails, 3 coloured dwarfs, 

 and I white dwarf. For this is the only ratio 

 which satisfies the conditions that the tails should 

 be to the dwarfs as 3 : i, and at the same time the 

 coloured should be to the whites as 3 : i. And 

 these are the proportions that Mendel found to 

 obtain actually in his experiments. Put in a more 

 general form, it may be stated that when two indi- 

 viduals are crossed which differ in two pairs of 

 differentiating characters the hybrids (F^) are all 

 of the same form, exhibiting the dominant character 

 of each of the two pairs, while the F, generation 

 produced by such hybrids consists on the average 

 of 9 showing both dominants, 3 showing one 

 dominant and one recessive, 3 showing the other 

 dominant and the other recessive, and i showing both 

 recessive characters. And, as Mendel pointed out, 

 the principle may be extended indefinitely. If, for 

 example, the parents differ in three pair of characters 

 A, B, and C respectively dominant to «, b, and c, the 

 F individuals will be all of the form ABC, while 

 the Fj generation will consist of 27 ABC, 9 ABc, 

 9 AbC, 9 aBC, 3 Abe, 3 aBc, 3 abC, and i abc. 

 When individuals differing in a number of alternative 

 characters are crossed together, the hybrid generation, 

 provided that the original parents were of pure 

 strains, consists of plants of the same form ; but 

 when these are bred from, a redistribution of the 

 various characters occurs. That redistribution follows 

 the same definite rule for each character, and if the 

 constitution of the original parents be known, the 

 nature of the F^ generation, i.e. the number of 

 possible forms and the proportions in which they 



