An Introduction to a Biology 



inferior vigour of its mate, and in impressing its charac- 

 teristics in their entirety on their offspring. It might be 

 thought that a tall pea dominates over a dwarf pea because 

 the tall has greater constitutional vigour. But, as I have 

 already pointed out, this is not the case. Dominance and 

 recessiveness belong not to the individual as a whole, but 

 to the distinct characters of the individual. We could not 

 prove this to be so in the case of crosses between individuals 

 differing in respect of a single pair of characters only ; but 

 we can prove it up to the hilt in the present case of a cross 

 between two individuals differing from one another in respect 

 of two pairs of characters — the shape of the comb and the 

 colour of the plumage. Of the two dominant characters 

 shown by the hybrid, rose-comb and white plumage, one 

 comes from the Black Hamburgh and the other comes from 

 the White Leghorn. So there is no question here of one of 

 the parents impressing its characters as a whole on its off- 

 spring. The reason that the Black Hamburgh transmits its 

 rose-comb to the hybrid cannot be because it has greater 

 constitutional vigour than the White Leghorn, because the 

 Black Hamburgh fails to transmit its black plumage. Simi- 

 larly, the abihty of the White Leghorn to transmit its 

 white plumage to the hybrid cannot be due to its greater 

 constitutional vigour, because it cannot transmit its single 

 comb. 



You may say, if you like, that the Black Hamburgh was 

 prepotent with regard to its comb, and the White Leghorn 

 with regard to its colour ; but if you do you are merely 

 expressing the Mendelian idea of dominance in terms of pre- 

 potency. The truth is that dominance has nothing to do 

 with the individual at all ; it relates solely to the separate 

 characters which we can deal with in breeding — colour of 

 plumage, shape of comb, etc. ; and this brings us to the 

 very essence of the Mendelian doctrine, which is, that in a 

 scientific principle of breeding, attention must be paid not 

 to the individual as a whole, but to its various characters, 



275 



