Menders Law 53 



BLENDS 



This t^pe of inlieritance when first discovered was 

 thought to be in direct conihct w-ith Mendel's law. It 

 is a case in which dominance seems to fail, for the two 

 alternative characters both express themselves and the 

 result is an average between them. It is easy to explain 

 this situation in accordance with the presence and 

 absence h}'pothesis without any violation of Men- 

 del's law. 



The classic example of blending inheritance was 

 presented by Correns (i) in breeding work upon Mira- 

 hilis Jalapa, the common four-o'clock. Correns crossed 

 red-flowered and white-flowered varieties, and all the 

 hybrid progeny had rose pink flowers. This was a color 

 blend, distinctly intermediate between the colors of the 

 two parents. The Fi generation, therefore, seemed to 

 contradict Mendel's law in that one color character was 

 not completely dominant over the other. The real 

 situation, however, appeared in the F^ generation 

 obtained by inbreeding individuals of the Fi generation 

 which showed the blend. By inbreeding the pink 

 hybrids Correns obtained the perfect 1:2:1 ratio, that 

 is, I red like one grandparent, 2 pink like the hybrid 

 parent, and i white like the other grandparent. Segre- 

 gation was evidently taking place, the only unusual 

 thing being the appearance of the Fj individuals, and 

 that was explained immediately as failure of dominance 

 (see fig. 8). 



The question this introduces, therefore, is that of a 

 mechanism which would account for such a result. The 

 easiest explanation offered is that the red parent was a 

 homozygote for redness (double dose) and the hybrid 



