Meiotic metaphase I pairing behavior of a 5BL recombinant isochromosome inwheat

A recombinant isochromosome i5BL(rec) of wheat was developed with one arm a nd the proximal 36% of the other arm of Chinese Spring (CS) origin and the distal 64% of the recombined arm of Triticum turgidum subsp. dicoccoides or igin. The i5BL(rec) provides an unusual opportunity to analyze the role of the centromere or arm heterozygosity in chromosome prealignment and synapsi s during meiosis. In monosomic condition, the i5BL(rec) formed a ring univa lent in 86.8% of the pollen mother cells (PMCs) at meiotic metaphase I. In the disomic condition, the two i5BL(r)ec preferentially paired as a normal bivalent in 74.8% of the PMCs, which differed significantly (p <0.01) from the normal bivalent pairing of 51% observed in diisosomic 5BL chromosomes o f the CS (Di5BL(CS)) control plants. In plants with one i5BL(rec) and a nor mal 5B(CS), the long arm of 5B(CS) paired with the homologous arm of i5BL(r ec) in 54.4% of the PMCs, and 40.4% of the PMCs had a 5B(CS) univalent and a i5BL(rec) ring univalent. The implications of the i5BL(rec) pairing data on the mechanism of Ph1 gene action are discussed.