THE PROBLEMS IN MATING AND IN EGG PRODUCTION 121 



the Blue Andalusian fowl. It is difficult to secure a slaty-blue 

 color, with darker hackle and with dark lacing of feathers on 

 the breast. The off colors are white splashed with black and 

 blacks. 



By making a careful study in breeding these blues it will be 

 found that there will always be produced one black, one 

 splashed white, and two blues; the blues are heterozygous, 

 and the splashed whites and blacks are homozygous, forms. 



If the whites are bred together they will be found to always 

 breed white. Likewise, if the blacks are bred together they 

 will always breed black, but if the blacks and white are bred 

 together they produce nothing but blues; that is, the off colors 

 breed twice as many blues as when the blues are bred together. 

 Therefore the blacks and the whites are the pure breeds, while 

 the blue is a mongrel who can never be bred so as to always 

 breed true. 



There are a few instances where a visible distinction can be 

 drawn between a pure dominant and a heterozygote. Certain 

 white breeds, as the White Leghorn, in which white behaves 

 as a dominant color; heterozygous whites, made by crossing 

 the dominant white birds with pure colored forms, as the 

 Brown Leghorn or even the Spangled Hamburg, almost in- 

 variably show ticks in their plumage. 



This shows the white dominance is not quite complete in 

 the White Leghorn 



Punnett suggests that the dominant white fowl may be a 

 colored bird plus a factor which inhibits the development of 

 the color. 



The Spangle in the Silver Spangled Hamburg is a gen- 

 etic factor and is carried in the sex chromosome of the male. 

 It follows the sex link of inheritance. 



MONOHYBRIDISM AND DIHYBRIDISM 



Mated pairs differing only in a single pair of characters are 

 known as cases of Monohybridism. Where the original parents 

 differ in two pairs of characters the case is termed one of 

 Dihybridism. 



Take the case of a cross between the rose-comb Black 



