MENDEL'S LAW 231 



excessive size of the comb and its becoming frosted, the produc- 

 tivity of the individuals was impaired. He desired to remedy this 

 by replacing the single comb with a pea comb, but in order to do 

 this it would be necessary to cross his birds with Indian Games 

 possessing finely developed pea combs. The pea-comb trait 

 would be fixed in the early generations, since this is a dominant 

 character. It would require, however, many generations of breed- 

 ing and selection to eliminate the color pattern which was brought 

 into the flock by the intermixture of the game blood. 



In a study of characters which may possibly result from hybrid- 

 izing and the frequency of their occurrence, knowledge of Mendel's 

 law will be helpful. 



Mendel's Law. Mendel's law states that, when crossed forms 

 or hybrids are bred together the opposing characters possessed 

 by the original parents tend to combine in definite proportion. 

 The offspring from such hybrid individuals (AB) will assume the 

 algebraic form A 2 +2 AB-f-B 2 . In the formula A represents one 

 of the contrasting characters, while B represents the opposite 

 trait. This formula means, in numbers, that, out of every 100 

 chicks resulting from a cross, twenty-five will possess one of the 

 characters, or will be pure A, twenty-five will be pure B, while 

 the remaining fifty (represented by the figures 2 AB) will be a 

 mixture of the two opposing characters. 



Mendel's law also states that where there is a pair of contrast- 

 ing characters, for example, single comb and rose comb, one 

 will be dominant over the other, the result being 'that a majority 

 of the progeny will show this dominant character. The other 

 opposing character is termed recessive, for it recedes from view in 

 the presence of the stronger or more prominent one. Dominance 

 of a character does not imply that the recessive one is absent, 

 but simply that in the development of the new individual the 

 dominant character is bound to appear. A pigmented condition 

 of the plumage is dominant over absence of pigment; an extra 

 toe is dominant over a normal number; feathers on the shanks 

 are dominant over their absence, the rose comb over the single 

 comb, and so on through a great variety of characters. Only one 

 pair of contrasting characters is to be considered at any one time. 

 This second phase of Mendel's law may be expressed by the fol- 

 lowing formula: 



D 2 +2 Dr+R 2 



