110 



GENETICS AND EUGENICS 



Attempts of poultry men to " fix " the blue variety are mani- 

 festly hopeless, unless some new variation arises within the 

 race which can be secured in homozygous form and will yet 

 possess the desired appearance. 



Another example of a heterozygous and so unfixable char- 

 acter is found among short-horn cattle. Here red is a true- 



/\iTdbiUs Jalajia 



Fig. 51. A diagram to show inheritance of flower color in crosses of Mirabilis, the " four-o'clock." 

 Alha, white parent; rosea, red parent; alba + rosea, the unfixable Fi heterozygote, of intermediate 

 color, pink. I. Gen. = Fi. U. Gen. = F2. (After Correns.) 



breeding type as also is white, but the heterozygote between 

 red and white is an unfixable roan. (See Figs. 62-64.) 



The effect which the production of a recognizable hetero- 

 zygous form has upon the typical F2 monohybrid ratio 

 (3:1) is to convert it into a 1:2:1 ratio, in which each 

 parental type is represented by one individual while the 

 heterozygous type is represented by two. The typical di- 



