The Behavior of Interchange Heterozygotes in Oenothera

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Abstract
The differences between gametic complexes in complex heterozygotes in Oenothera are associated with structural changes and cannot be resolved into differences between independently segregating genes. When a ring of 4 is increased to a ring of 6, interchanges occur between the arms of 2 chromosomes in opposite complexes and result in the presence of interstitial homologous segments in chromosomes with non-homologous ends. The genes in these relatively translocated segments normally do not cross-over because of their position after translocation and because they are next to the spindle attachment; they cause the essential differences between complexes. The number of chromosomes in a ring is increased by successive interchanges, each of which gives one such new, relatively translocated segment in each complex. Within the ring associations each interchange between segments in opposite complexes will produce reduplications and corresponding deficiencies. If deficiencies of short segments be lethal to the gametes of one sex only, heterogamy results. Pairing in haploids demonstrates reduplications within a complex. New zygotic types (half-mutants and mass-mutants) arise from gametes in which secondary interchange has been produced by crossing-over in the relatively translocated segments. This crossing-over is infrequent because of the structural heterozygosity.

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