FIXING GOOD TRAITS 27 



In this particular generation the quality of 

 bigness prevails because bigness is dominant to 

 smallness. But the factor for smallness must 

 have a hearing in the next generation. 



Until we can produce a white blackberry that 

 is "homozygous" for size factors as well as for 

 color factors, we shall not obtain a fruit that will 

 breed true to size as well as color. 



A similar analysis might be applied to the 

 various other pairs of unit characters that are 

 represented in any given fruit or flower. And 

 the essential principle, stated in Mendelian 

 terms, to be aimed at by the experimenter who 

 would fix a newly developed type of plant so 

 that it will breed true from seed, must be to 

 render the plant "homozygous" for the factors 

 of each pair of unit characters involved. If that 

 can be done, the plant will breed true; if that 

 cannot be done, the plant will not breed true. 



In the olden phrasing, this would be spoken of 

 as "line" breeding a method long familiar to 

 every breeder of plants or animals. 



FIXING A TYPE IN THE SECOND 

 GENERATION 



In actual practice, where only two or three 

 unit characters are involved, it may be possible 

 to produce a new type that breeds true, or is 



