i86 



THE BEHAVIOUR OF POLYPLOIDS 



In Primula kewensis the corresponding chromosomes of the 

 diploid parents, P.florihunda and P. verticillata, are not sufficiently 

 different to inhibit their pairing in the diploid hybrid. Such a lack 

 of differentiation is associated with two abnormalities in the 

 tetraploid : (i) Chromosomes of opposite parents occasionally pair 

 (in quadrivalents or bivalents) and pass to opposite poles. The 

 progeny therefore differ in the proportions of the chromosomes of 



Ger/v 

 AfaMer- 

 Cells 



Two 

 Cells. 



Four 

 Poller 



Grairts 

 or 



/e/nale 



5/^ores. 



Fig. 64, — Diagram showing how chromosomes pair and segregate in 

 a sterile diploid hybrid, such as Primula kewensis, by somatic 

 doubling and in the fertile tetraploid derived from it (neglecting 

 the consequences of crossing-over). The first gives various 

 new (untested) combinations of chromosomes, the second gives 

 uniformly the same combination that the parent had. (From 

 D., 1932 h.) 



the two species present. Moreover, owing presumably to this pairing 

 being accompanied by crossing-over the normal type can never 

 again be recovered from its aberrant offspring, (ii) Quadrivalents 

 are formed which sometimes divide unequally (as in the auto- 

 tetraploid Dahtra, Primula sinensis and Dadylis), giving, therefore, 

 gametes with 17 and 19 chromosomes instead of 18, and progeny 

 with 34, 35 and 37 chromosomes instead of 36. These differ from 

 the normal tetraploid both owing to a change in proportion within 



