An Introduction to a Biology 



two individuals differing from one another in respect of a 

 single pair of characters are mated. We have now to con- 

 sider the results of mating two individuals which differ from 

 one another in respect of two pairs of characters. This is a 

 very important case, because on it depends the efficient 

 carrying out of one of the most important processes of the 

 breedor namely, the combination in one strain of char- 

 acters already existing in separate strains. The behaviour, 

 on crossing, of two very well-known characters of the fowl 

 may be used to illustrate this point. The two pairs of cha- 

 racters will first be considered separately. One pair relates 

 to the colour of the plumage ; and the pair consists of white 

 and black, white being dominant over black. The other pair 

 relates to the shape of the comb, and consists of the so-called 

 " rose "-comb (of Wyandottes and Hamburghs) and the 

 single comb (of Minorcas and Leghorns) of which the " rose " 

 is dominant over single. Let us now describe an actual case 

 in which these two pairs of characters are concerned. Such 

 a case is a cross between the Black Hamburgh, which, as its 

 name implies, is black, and like all the Hamburghs has a 

 rose-comb, and the White Leghorn, which is white, and has 

 a single comb as shown, very diagrammatical ly, in Fig. 3. 

 White being dominant over black and " rose " over single, 

 the hybrid produced by crossing the parent forms described 

 above should have white plumage and a rose-comb, and it 

 actually has. I bred many such hybrids last year. In pass- 

 ing, it may be remarked that this result shows very clearly 

 the profound difference between dominance and a thing to 

 which the name " prepotency " has been given. A prepotent 

 animal is one which is supposed to have the power of impress- 

 ing its characteristics on all its offspring, whatever it is 

 mated with. It is usually a particular stallion or bull which 

 acquires the reputation of prepotency. This prepotency is 

 supposed to be due to the exceptionally great constitutional 

 vigour of the prepotent animal, a vigour which has no diffi- 

 culty in overcoming the feeble opposition offered by the 

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