I 



CHAPTER XI 



HOW CHARACTERS BEHAVE IN TRANSMISSION 



Characters tend to combine in definite mathematical proportions • Characters 

 that do not blend • Mendel's law of hybrids • Dominant and recessive 

 characters • Pure races may spring from crossing • Very few individuals 

 pure • A second method of improvement • Improvement by hybridization 

 complicated • Mutation and mutants • Origin of new and improved strains 



The manner and machinery of transmission are exceedingly 

 simple, but the mystery is, how so many and such different unit 

 characters are contained in so small a bit of living matter, for 

 that is all that passes over from parent to offspring. Many 

 ingenious theories have been offered in explanation, but the 

 mystery itself has never yet been solved. We do know much, 

 however, of what in the end really happens, and in that, after 

 all, the chief practical interest lies. 



Characters tend to combine in definite mathematical propor- 

 tions. In the .case of the white and yellow corn, for example, 

 if a yellow silk is fertilized by a white pollen grain, the resulting 

 kernel will be a " half blood " ; that is, one half its color tenden- 

 cies will be yellow and one half white. If such a kernel now be 

 planted where its progeny will again be fertilized by white pollen, 

 the result will be a three-fourths white and one-fourth yellow 

 generation. If the same be done again, the next generation 

 will have seven eighths of the white " blood " with only one 

 eighth remaining of the yellow, and so on indefinitely in regularly 

 increasing and decreasing proportions. Of course the opposite 

 result, but on the same plan, would have followed if the half 

 blood had been bred successively with yellow rather than with 

 white varieties. 



Having found the principle, we can readily calculate the 

 " blood " of the progeny of any known mixture. For example, 



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