205 



of the admixture which we would expect to find resulting from 

 the cross. Extensive experiments in breeding showed that 

 the results were to be interpreted as follows : 



RESULTS. 



"A gray mouse 'G' bred with a white mouse 'W gave off- 

 spring which seemed to be all gray, but were really a mixture 

 of gray and white, the gray character being 'doniinaiif and 

 the white character 'obscured' or ''recessive,' as Mendel called it. 



"That is G X W gave: G (W), G (W), G (W), etc., the 

 parenthesis indicating that the white character was recessive. 

 This hidden complex nature of the second generation (the 

 young from the first cross) was clearly indicated when they 

 were bred together. It was found that their offspring was of 

 three sorts, and that, these three kinds were in definite and 

 numerical proportions. 



"G ( W) X G (W) gave offspring : 



"i G + 2 G (W) + I W : one-fourth being pure gray, one- 

 fourth pure white, and one-half apparently gray, but really as 

 further breeding showed, gray and white, the white character 

 being recessive and obscured. These numerical proportions 

 held true for an exrensive series of experiments in the case of 

 white mice, as they had done in the experiments of Mendell 

 upon certain plants-" 



SPORTS. 



"Very divergent individuals which arise by variation are 

 commonly called 'sports.' It is easy to see that if a single 

 brood of sports arose which were especially well adapted to 

 their environment, although they might breed with non- 

 divergent individuals of the species, yet among the offspring 

 of the third generation there would be individuals like the 

 original sports." 



From this statement of the rule it is evident that the breeder 

 can by selection change the character of the species from the 

 old type to the new type (represented by the sport) by selec- 

 tion and elimination. 



It should- be stated tliat Mendel, and Dr. Castle and others 

 who succeeded him found the rule not without exception, for 

 Dr. Castle found that in breeding white and gray mice, that a 

 certain proportion of the offspring from the first cross were not 

 gray or white, but dappled gray and white, and not as we 

 would expect from Mendel's Law. 



Having given a bird's-eye view of the subject let us go more 

 fully into Mendel's experiments in detail. 



