XIV 



INTERMEDIATES 



165 



that four separate factors are concerned, of which 

 each, when present, leads to a definite increase in 

 weight. It must be supposed also that a factor 

 produces a greater effect in the homozygous than 

 in the heterozygous condition. To account for 



600 700 800 900 1000 1 100 1200 1300 1400 1500 i6oo 



Sel?right 



99 



r- 



T. 



J 



99 ^ 



(weight' 



'ed) 



U 



tti 



!•• 



Hamburgh 



^(^ 



••••••• ••••••• 



.••••• ••••• 



I 



I 



Fig. 46. 



Graphic representation of weight distribution in Fi and F2 generations from 

 Sebright-Hamburgh cross. Each black dot represents an individual, and is 

 placed according to its weight in grams. 'Ihe weights of the males only are 

 given in F.^. The weights assigned to the female parents are Jths their actual 

 weights. They have been "weighted" in this way because the normal weight 

 of a hen in these strains is on the average about |ths of the weight of the corre- 

 sponding cock. 



the appearance in P., of birds smaller and larger 

 than the original parent breeds, we may suppose 

 that the Hamburgh contained three of these four 

 size factors, and that the Sebright contained the other 

 one. Segregation and consequent recombination 

 in F would result in the production of some birds 



