The Genetic Control of Mutability 



219 



produce more than one quarter of Fi that are 

 lights and correspondingly fewer that are 

 medium. 



Other properties of Mp have been dis- 

 covered. Mp may become fixed at the P 

 locus, so that a medium becomes a stable 

 nonred form. Transposed Mp may occupy a 

 variety of sites, two of which have already 

 been mentioned (linked, and no longer 



hnked, to chromosome 1). In 57 of 87 cases, 

 transposed Mp was still linked to chromo- 

 some 1, having moved less than 50 crossover 

 units from P. In the remaining cases Mp 

 was transposed to any one of five different 

 nonhomologous chromosomes. Of the 57 

 cases where transposed Mp was still linked to 

 chromosome 1, 37 cases showed Mp within 

 five crossover units of P, 10 were between 



/, 



PHENOTYPE 



GENOTYPE 



Medium 

 Variegated 



r w 



P Mp / P 



Mutants 



Red 



r w 



P /P 



Light ^ r w 



Variegated P Mp / P + Transposed Mp / - 



FIGURE 25-6. New genetic liypothesis 

 for pericarp variegation. 



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