SEGREGATION AND RECOMBINATION IN TRISOMICS: A RECONSIDERATION

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Abstract
Segregation amongst the diploid progeny of heterozygous trisomics of secondary, tertiary, compensating, and telo types can be modified if crossing over takes place between the extra and normal chromosomes and between the centromere and the locus of the gene in question. Although the deviations from normal Mendelian ratios are small and are minimized by such factors as propinquity of the locus to the centromere, certain types of disjunction, and failure of pairing of the extra chromosome, they can be large enough to be detected in populations of the size normally used for testing trisomic segregation. Examples are cited from the segregation of tomato tertiary and telotrisomics in which the majority of distally located markers show the expected deviations.