Induced interchange heterozygosity in diploid Chrysanthemum

Summary Following a programme of recurrent irradiation and planned hybridization, it has been possible in Chrysanthemum carinatum to synthesise an interchange stock in which 12 of the 18 chromosomes are involved in rearrangements and form a single multiple association during meiosis. Induced interchange heterozygosity of this type has been made use of for studying the relationship between fertility and meiotic behaviour. Relatively high fertility of the interchange heterozygotes was found to be mainly due to a pronounced tendency of the interchange multiples to show preferentially a particular type of orientation at metaphase. Factors governing the orientation of multiple association resulting from interchange heterozygosity have been discussed.