The molecular features of chromosome pairing at meiosis: the polyploid challenge using wheat as a reference

During meiosis, chromosome numbers are halved, leading to haploid gametes, a process that is crucial for the maintenance of a stable genome through successive generations. The process for the accurate segregation of the homologues starts in pre-meiosis as each homologue is replicated and the respective products are held together as two sister chromatids via specific cohesion proteins. At the start of meiosis, each chromosome must recognise its homologue from amongst all the chromosomes present in the nucleus and then associate or pair with that homologue. This process of homologue recognition in meiosis is more complicated in polyploids because of the greater number of related chromosomes. Despite the presence of these related chromosomes, for polyploids such as wheat to produce viable gametes, they must behave as diploids during meiosis with only true homologues pairing. In this review, the relationship between the Ph1 cyclin-dependent kinase (CDK)-like genes in wheat and the CDK2 genes in mammals and their involvement in controlling this process at meiosis is examined.