An Introduction to a Biology 



which can be shown to be inherited independently of one 

 another. 



We shall see what this means if we observe what happens 

 when the white, rose-combed hybrids, between the Black 

 Hamburgh and White Leghorn, are mated together. If a 

 sufficiently large number of chicks is hatched out we shall 

 find all the four possible combinations of the two pairs of 

 characters, white and black plumage, and rose and single 

 comb, in the order shown in the diagram, Fig. 3 ; and in the 

 proportions indicated — 9 white, rose ; 3 black, rose ; 3 

 white, single ; and 1 black, single. The numbers indicate 

 the average number of each combination in every 16 birds ; 

 but, of course, there would have to be many more than 16 

 birds to get anything like a close approximation to these 

 actual proportions. But the proportions are not the essen- 

 tial fact, though they are very important. The essential 

 fact is that all possible combinations of the characters borne 

 by the parents do occur in the second hybrid generation. 

 This reveals an important fact and teaches an important 

 practical lesson. The fact which it reveals is that the shape 

 of the comb and the colour of the plumage of, for instance, the 

 Black Hamburgh, are not transmitted in conjunction, but 

 can be separated from one another by cross-breeding, so 

 that, for instance, the black plumage of the Black Hamburgh 

 can be taken up as an independent element and united with 

 the single comb of the White Leghorn, and be permanently 

 combined as in the last bird on the right at the bottom of 

 Fig. 3. The principle of recombining characters in breed- 

 ing is of course not a new one — it must have been done un- 

 consciously, and has probably been done deliberately ; but 

 a familiarity with the simple scheme given in Fig. 3 will 

 greatly facilitate the process of the recombination of cha- 

 racters. 



The important lesson to be learnt from the fact that all 

 possible combinations of the parental characters occur in the 

 second hybrid generation we are considering, is that this 



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