CHAPTER IX 



GAMETIC COUPLING AND SPURIOUS ALLELOMORPHISM. 



Pollen-Shape and Flower-Colour. Axil-Colour and Sterile 

 Anthers Hooded Standard and Flower-Colour in 

 Sweet Peas. 



WE have. now to consider one of the most curious and 

 interesting developments of Mendelian research. In all 

 the examples hitherto described the F^ numbers have shown 

 that when allelomorphs belonging to various pairs are simul- 

 taneously distributed among the gametes in the process of 

 gametogenesis, the distribution is random, so that all possible 

 combinations are represented by equal numbers of gametes. 

 For example, in the case of the double heterozygote formed 

 by crossing a yellow, round pea with a green, wrinkled 

 variety, the gametes produced by the F^ plant are in equal 

 numbers bearers of 



(1) yellow, round, 



(2) yellow, wrinkled, 



(3) green, round, 



(4) green, wrinkled. 



This fact is proved by the numbers 9:3:3:1 in 

 which the several types of zygotes appear in F. The 

 phenomena now to be described indicate a system of segre- 

 gation taking place in such a way that gametes presenting 

 certain such combinations occur with greater frequency than 

 the others. 



The example in which this state of things was first 

 detected is that of the pollen-shapes of the Sweet Pea 

 (Lathyrus odoratus]. The experiments in that case were 

 begun, as has already been described (p. 89), by crossing 

 a white Emily Henderson having long pollen, with a white 



