Dosage Effect of the Ph1 Locus on Homologous Crossovers in a Segment of Chromosome 1B of Bread Wheat (Triticum aestivum L.).

Introduction: The Ph1 locus in polyploid wheat enforces strictly bivalent behaviour in meiotic metaphase I, by preventing homoeologues from crossing over. It has always been considered as completely dominant as no homoeologous metaphase I pairing has ever been detected with its single dose present. However, Ph1 also affects pairing and crossing over of homologous chromosomes.

Methods: Homologous crossover frequencies with Ph1 in two, one, and null doses were scored cytologically, as exchanges within a ca. 9.5-9.9 Mbp terminal wheat segment of a wheat-rye translocation T-9 and corresponding segments in chromosome arms 1BS originating from four wheat cultivars.

Results: In all cases, the crossover rates in the tested homologous segment of wheat genome, with a single dose of Ph1 present, were intermediate between those at two and null Ph1 doses. Averaging across all four chromosomes, the crossover rate with a single dose of Ph1 present was 37% higher from that with two doses and 46.4% lower of that with a zero dosage.

Conclusion: The Ph1 locus in wheat affects homologues and appears to operate in a dosage-dependent manner.