298 



ANIMAL BIOLOGY 



mediates, really exhibit the characters of both parents: neither 

 character is recessive. Thus in Shorthorn cattle, red and white 

 when mated give roan, a color effect resulting from a close inter- 

 mingling, or mosaic, of red and white hairs in the coat. Accordingly 

 roan Shorthorns are always heterozygous, but their offspring give 



o o 



f, 



Fig. 186. — Diagram to illustrate the results from crossing white and red 

 flowered races of Four-o' clocks, Mirabilis jalapa. The somatic condition 

 (phenotype) is shown graphically; the small circles represent the genes which 

 are involved. 



the expected ratio of 1 red : 2 roan : 1 white which is clear evidence 

 of segregation. Another example is the well-known blue Andalusian 

 fowl. This will not breed true — it is a hybrid in which the charac- 

 ters of both parents are exhibited, apparently not blending though 

 giving a somewhat intermediate effect. Its offspring show the 

 ratio of 1 black : 2 blue Andalusian : 1 white-splashed-with-blue. 

 In order to obtain all blue Andalusians — the type recognized by 

 poultrymen — it is necessary to mate black with white-splashed- 



