HOMOEOLOGOUS CHROMATIN EXCHANGE IN A RADIATION-INDUCED GENE TRANSFER
Some of the ionizing-radiation-induced translocations between alien and wheat chromosomes show no deleterious effects and are transmitted normally through the pollen. Translocations of this type will be called "compensating". In one such compensating translocation, designated T4, a segment of Agropyron elongatum (Host.) P.B. chromosome 7el1 with gene Lr19 controlling resistance to leaf rust was transferred into wheat chromosome 7D. The T4 translocation was found to have involved chromosome arms 7el1α and 7DL. The pairing relationships of Agropyron telosome 7Eα with telosomes 7AL, 7BL, 7DS and 7el1α was studied in wheat-Aegilops speltoides Tausch. hybrids. The 7Eα telosome paired with 7DS and, therefore, is homoeologous with it. It did not pair with 7AL, 7BL, and 7el1α. Hence 7AL, 7BL, 7DL, 7el1α must be homoeologous. Consequently, chromatin in the long arm of chromosome 7D was replaced with homoeologous chromatin of the Agropyron chromosome in the T4 translocation.