FUTURE OF THE SCIENCE OF BREEDING 161 



of the whites are without it. For this something, whatever it 

 may be, we use the term factor, and it is with respect to these 

 factors that we term the gamete " pure." Whether these 

 factors are really permanent and indivisible without losing 

 their distinctive properties, in the sense that chemical mole- 

 cules are permanent and indivisible, or whether they can 



Fio. 3. — Diagram showing^^the result of mating a heterozygous black 

 with the reoessiTe white. Equal numbers of black and white chicks are 

 produced, and all of the blacks are heterozygous. 



be fractionated, is a question on which, at present, there 

 is a difference of opinion, as we shall see later. For the 

 moment we will assume that they are definite indivisible 

 entities. 



We spoke of the first-cross Rosecombs as forming only 

 gametes of the two parental types, and in this particular case 

 it is true. But every breeder knows that when first-cross 

 animals are bred together, however pure the parental strains 

 may have been, the progeny are usually exceedingly diverse. 



M 



