GENETIC BASIS 



33 



actually observed among 347 F2 plants. In figure 4 these 

 same data are combined into a three-way correlation diagram 

 showing the relation between total recombination for these 

 three characters and the actual recombinations obtained in 

 the experiment. A comparison of figures 2 and 3 with figure 

 4 will show that the mathematical deductions are indeed 

 correct. The second generation extremes which at first 



Fig. 3. Actual extreme recombinations, diagrammed to scale, obtained 

 in a large F2 between N. Langsdorffii and A^. alata. A' is the closest ap- 

 proach obtained to the theoretical extreme A of Fig. 2, B' the closest to 



B, etc. The letters refer to Fig. 4. 



seemed so variable become impressively uniform when com- 

 pared to the imaginary recombinations of figure 2.'^ (An- 

 derson, 19396). 



THE RECOMBINATION SPINDLE 



These data demonstrate that the recombinations of the 

 F2, however manifold they may seem, are in reality but a 

 narrow segment of the total imaginable recombinations of the 

 parental species. If we think of all the characters of one 

 species being represented at one of the apices of a multi- 

 dimensional cube and all the characters of the other species 

 at the opposite apex, then the recombinations that we get 

 in the F2 form a narrow spindle through the center of the 

 cube. In morphological language, though we have a great 



