The Theory of Polymery 



351 



of loci and others are almost, if not entirely, homozygous, al- 

 though they might be of the same size because they contain 

 the same number of contributing genes. In this study of corolla 

 length, families 1, 2, and 7 of the F3 generation show little 

 variability, family 3 shows a little more, and 4, 5, and 6 are 

 much more highly variable. 



16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 88 91 94 97 100 



Fig. 98. Frequency curves for length of corolla tube in Nicotiana. Left, 

 N. Langsdorffii ; right, N. alata; center, the Fi and F2 from a cross between 

 these two species. Note that the means of the Fi and F2 are about the 

 same but that the Fo shows much greater variabiHty. (Redrawn from 

 East in Genetics.) 



According to the theory of polymery, all the Fi plants should 

 be genetically alike and, therefore, all the F2 families should be 

 of the same average size and should show the same amount of 

 variability. In other words, smaller Fi individuals should not 

 produce an F2 population with any lower average size than 

 larger Fi individuals. To test this out. East raised five F2 fam- 

 ilies, each of which came from an Fi plant of different size. He 

 found that the average size of all the F2 families was very 

 similar, and there was no correlation between the size of the Fi 

 plant and the average of the F2 family from it. All in all, this 

 cross between two plants of different length of corolla agrees 

 rather well with the theory of polymeric genes. 



