No. 609] 



THE THEORY OF THE GENE 



515 



For example, when peas that are both yellow and round 

 are crossed to peas that are both green and wrinkled, 

 there appear in the second (Fo) generation not only the 

 original combinations, yellow round and green wrinkled, 

 but also the recombinations yellow wrinkled and green 

 round. Here also the numerical results, 9:3:3:1, can 

 be explained by two assumptions, viz., that, as before, 

 each pair of characters (or their representatives) are 

 separated in the germ cells of the hybrid (Fi) and that 

 each pair "assorts" independently of the other pair. Ob- 

 viously, here, it can no longer be the wholes of the original 

 germ plasms that separate, for the two pairs of char- 

 acters behave independently of each other ; but there must 

 be separate pairs of elements in the germ plasm that 

 assort independently of one another. 



As a matter of fact it has been found that the many 

 pairs of characters that follow Mendel's law arc iiido- 

 ])endent of each other in inhci-itniKM'. 'riic only i-csti'ict ion 

 that this statenuMit mlU I'oi' i^ in llx- cnM' cf linked pnii- 

 of characters of which 1. shall speak later. 



The gci'in plasm must, therefore, l)e made up of inde- 

 pendent elenienls of some kind. It is these el(Mnent< that 

 we call iicnetie i'aetors or more briefly genes. 



This evideiice teaches us nothing further al)0ut the 

 nature of the ])ostulated genes, or of their location in the 

 germ plasm. However, even if we postulated nothing 

 more about them than their independence of each other 

 and their distribution in the genu cells, we could still 

 handle the Mendelian results on n purely inatliemntic;i I 

 basis that would enable us to predict what ih^w ( (Mnhinn- 

 tions should give. This possibility ah>n(^ would entirely 

 jnstify tiM' hypothesis as a scientific procedure, wliatever 

 cnrpiii- cMtic. ni.iN ^:iy to the contrary. Tn fact ^rendel 

 hiinx'lt' (lid not c.iri'y his analysis beyond this ])oint, for 

 he assnmeil only thnt definite ])aired elements that stand 

 in some way tor the eliaracters of the finished plant exist 

 in the gei in i)lastn. and that the j)airs assort independently 



