Artificial allotetraploidization is the derivation of synthetic allotetraploids. In an allotetraploid, chromosomes of similar genomes pair with their homologues in similar genomes rather than with their homoeologues in the dissimilar genomes. The basis of this discrimination is not completely understood because the mechanisms of chromosome pairing are not adequately known. Sybenga has hypothesized the existence of special units of DNA (zygomeres) that are responsible for the initiation of synapsis of chromosomes during meiosis. Zygomeres, if they exist, should be detectable by preferential pairing studies. In the work reported here, trisome 3 maize plants had two standard chromosomes 3 marked with the genes al sh2 or al Sh2, and an odd chromosome 3 from a commercial inbred line (or derivatives thereof) marked with the dominant alleles A1 Sh2. In a previous study, three inbred lines (B41, Hy, and 38-11) were found to have chromosomes 3 that caused a great amount of preferential pairing. It may be assumed that they have different zygomeres than those of the standard chromosome 3. Hybrids between these inbred lines and hybrids between the inbreds and the standard were used as the donors of the odd chromosome. Segregation for preferential pairing (and presumably for zygomeres) was observed. The data can be explained on the basis of only two zygomeres per chromosome. Zygomeres should be able to be mapped as though they were genes.
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