PRINCIPLES OF GENETICS 5 



If a hybrid brown-eyed individual (Fi brown-blue) 

 marries a blue-eyed individual, half the children will have 

 brown, and half will have blue eyes (Fig. 4). 



There are other crosses that give, perhaps, a more 

 striking illustration of Mendel's first law. For instance, 

 when a red and a white-flowered four-o'clock are crossed, 

 the hybrid has pink flowers (Fig. 5). If these pink- 



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Fig. 4. 

 A ' ' back-cross " of a brown-eyed, Fj, individual, heterozygous for 

 blue eyes, to the recessive type, blue eyes, giving equal numbers 

 brown-eyed and blue-eyed offspring. 



flowered hybrid plants self-fertilize, some of their off- 

 spring (Fs) are red like one grandparent, some of them 

 pink like the hybrid, and others white like the other 

 grandparent, in the ratio of 1:2:1. Here one original 

 parental color is restored when red germ-cell meets red, 

 the other color is restored when white meets white, and 

 the hybrid combinations appear as often as red meets 

 white,' or white meets red. All the colored flowered plants 

 in the second generation taken together are to the white- 

 flowered plants as 3 : 1. 



