Despite possessing multiple sets of related (homoeologous) chromosomes, hexaploid wheat ( Triticum aestivum ) restricts pairing to just true homologs at meiosis. Deletion of a single major locus, Pairing homoeologous1 ( Ph1 ), allows pairing of homoeologs. How can the same chromosomes be processed as homologs instead of being treated as nonhomologs? Ph1 was recently defined to a cluster of defective cyclin-dependent kinase (Cdk)-like genes showing some similarity to mammalian Cdk2. We reasoned that the cluster might suppress Cdk2-type activity and therefore affect replication and histone H1 phosphorylation. Our study does indeed reveal such effects, suggesting that Cdk2-type phosphorylation has a major role in determining chromosome specificity during meiosis.