Abstract
Homoeology between the A and B genomes of allotetraploid (2n = 4x = 28) AiAiBiBiand autoallooctoploid (2n = 8x = 56) AIAIAIAIBIBIBIBIcytotypes of B. inermis Leyss. was studied in a tetraploid F1hybrid (AeAeAiBi) from 4x B. erectus × 4x B. inermis and in a haplo-triploid (AIeAIeBI) which occurred spontaneously in the F2from open-pollination among plants of the hexaploid F1hybrid (AeAeAIAIBIBI) from 4x B. erectus × 8x B. inermis. Chromosome pairing at metaphase I in both the tetraploid (AeAeAiBi) and haplo-triploid (AIeAIeBI) indicated that for each A genome chromosome there was a corresponding B genome homoeologue. There was no convincing evidence of gross structural differences between the two homoeologous genomes. The frequency of trivalent formation in the haplo-triploid was approximately one-half that found in two pentaploids (2n = 5x = 35) AIeAIeAIBIBI. This indicates that the pairing affinity between the A and B genomes is one-half that between homologues as expressed by trivalent formation in triploids of the type AAB and AAA. Homoeologous chromosome pairing (A with B) may be controlled by a gene which is hemizygous ineffective.
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