THE PRACTICE OF BREEDING 303 



be successfully applied in animal-breeding. This method, 

 like all the others described, is open to the objection that 

 it is after all based on mere chance. It is empirical and 

 unscientific. The proportion of failures to successes is 

 too great, and for these reasons it is a slow process of im- 

 provement. 



287. The mendelian method. The mendelian method 

 is based on the law of dominance and the segregation of 

 unit characters. The first step is to determine by the 

 behavior of the desired character in transmission whether 

 it is a dominant or a recessive character. If it is recessive, 

 then it is only necessary to combine two recessives, as 

 recessives are homozygous and always breed true. If 

 the desired character proves to be a dominant, it is first 

 necessary to determine whether it is present in a heterozy- 

 gous or a homozygous condition. If it is homozygous, it 

 will breed true. If it is heterozygous, by in-breeding and 

 gradually eliminating the recessives it is possible greatly 

 to increase the number of dominants appearing and thus 

 practically establish a pure strain. This method is also 

 more successful in plant- than animal-breeding. The 

 animal characters which have come to be recognized as of 

 value to man are generally complex and do not behave 

 in transmission as unit characters. 



