Wheat

Wheat refers to cereal grasses of the taxonomic genus Triticum, cultivated for their grain. Bread wheat, Triticum aestivum, exhibits allopolyploidy: its somatic cells contain six chromosome sets, conventionally written AABBDD, totaling $2n=42$. The letters distinguish three related ancestral genomes, each represented twice.^[ref]

This ancestry creates a problem during meiosis. A chromosome must normally pair and exchange DNA with its true homologous chromosome, rather than with a related chromosome from a different ancestral genome. The Ph1 locus helps stabilize that choice. In experiments comparing wheat with and without this locus, researchers used chromosome imaging and markers of chromosome synapsis and chromosomal crossover. Loss of Ph1 delayed synapsis relative to the stage at which chromosome ends cluster, allowing more opportunity for pairing between related chromosomes. The experiments also changed growth conditions and measured resulting crossovers.^[ref]

Polyploidy therefore involves more than carrying extra DNA: successful reproduction requires mechanisms that organize related chromosomes into reliably inherited sets.