The genome organization and diversification of maize and its allied species revisited: evidences from classical and FISH-GISH cytogenetic analysis

The present review summarizes our classical and molecular cytogenetic investigations in the genus Zea. The results obtained from the meiotic behavior analysis of Zea species and hybrids, confirm the amphiploid nature of all species in the genus, with a basic number of x = 5 chromosomes. All species with 2n = 20 are diploidized allotetraploids, whereas Z. perennis (2n = 40) is an allooctoploid with four genomes somewhat divergent from one another. These analyses also revealed the existence of postzygotic reproductive isolation among Zea species. Our studies using genomic in situ hybridization (GISH) provide evidence about the evolutionary relationships among maize and its allied species, and reveal remarkable genomic divergences. Particularly, knob sequences were not completely shared between taxa previously considered to be closely related. Our data strongly suggest that the teosinte Z. mays parviglumis is not the only progenitor of cultivated maize. Introgression of Tripsacum into cultivated maize cannot be discarded.