122 POULTRY CULTURE 



Hamburg and the single-combed White Leghorn. In this 

 case the rose-comb is dominant over the single-comb and the 

 white plumage is dominant over the black. 



Let the rose-comb be represented by R, dominant. 



Let the single-comb be represented by s, recessive. 



Let the white plumage be represented by W, dominant. 



Let the black plumage be represented by b, recessive. 



Then Rs X Rs = RR + 2Rs -|- ss, 



and Wb X Wb = WW + 2Wb + bb. 



i.e. when two hybrids are mated together the resulting pro- 

 geny (on the average) is one like the dominant parent, one 

 like the recessive and two with the qualities of both the domi- 

 nant and the recessive, i.e., in mating a white fowl with a 

 black fowl (in cases where the white is dominant), the result 

 will be one pure white (W), which will continue to breed white; 

 one pure black (b), which will continue to breed black; and 

 two white fowls, which carry black as a dominant or recessive 

 quality. These two are hybrids, which will breed the same 

 as their parents. 



What is true of white plumage appHes to the rose-comb. 



Dihybridism. — ^In the cross between the Black rose-combed 

 Hamburg and the White single-combed Leghorn we have a 

 case of dihybridism. The average result of such mating will 

 be shown by the algebraic formula 



(RR -I- 2Rs -t- ss) X (WW + 2Wb + bb) 



In working out this simple formula we may place the symbols 

 multiplied, in any order, thus WR, which expresses the domi- 

 nance of white plumage and rose-comb, is equally correct if 

 put down as RW. If I wish to express the white plumage I 

 put the W first, and the result is — ■ 



This shows that out of every 16 of the progeny there will be 

 on the average 12 chickens with white plumage and 4 with 



