Two lines of common wheat cv. Chinese Spring carrying mutant alleles for the Ph2 homoeologous pairing-suppressor gene on chromosome arm 3DS promoting homoeologous pairing in wheat interspecific and intergeneric hybrids have been tested for their mitotic sensitivity to colchicine. Both the ph2a mutation, which corresponds to a fairly long deletion of 3DS, and ph2b, which is either an intragenic change or a very small deletion, as well as the ph2a/ph2b heteroallelic combination and the deficiency for the entire 3DS arm (ditelo 3DL), conditioned a significantly lower sensitivity to colchicine than that determined by the wild-type allele Ph2 (euploid and ditelo 3DS). Observation of both metaphase and anaphse root-tip cell populations, treated with various colchicine concentrations, provided similar results. The degree of spindle disruption in 2 × 10−4 M colchicine, as measured by the percentage of fully affected metaphases (C type), was significantly reduced in ph2 and Ph2− genotypes and, consequently, a larger proportion of cells could proceed toward anaphase and also had a regular segregation pattern at this stage. The differential sensitivity of ph2 genotypes to colchicine is in the opposite direction to that previously found for ph1 genotypes, lacking the homoeologous pairing suppressor on chromosome arm 5BL. The ph2 mutation, while promoting homoeologous pairing as ph1 does, decreases spindle sensitivity to colchicine with respect to the wild-type (ph2) allele rather than increasing it, as ph1 does. The observed alteration of spindle sensitivity to colchicine that mutants for structurally unrelated but functionally related genes (Ph1 and Ph2) condition is interpreted as a highly probable coincidence in their cellular target. It is assumed therefore that these loci affect the equilibrium between tubulin and microtubules. Through this effect they presumably determine chromosome positioning in somatic and premeiotic stages, leading to different pairing patterns at meiosis. Key words: Triticum aestivum, tubulin, pairing suppressors, somatic association.
Profiling diverse sequence tandem repeats in colorectal cancer reveals co-occurrence of microsatellite and chromosomal instability involving Chromosome 8