Cytogenetic studies in the genus Zea. DNA content andheterochromatin in species and hybrids.

C.M. TITO, L. POGGIO Y C.A. NARANJO

THEORETICAL AND APPLIED GENETICS

SPRINGER

Año: 1991 vol. 83 p. 58 - 64

0040-5752

Summary. The nuclear DNA amount and the hete-rochromatin content in species and hybrids of Zea were analyzed in telophase nuclei (2C) of the root apex of germinating seeds. The results revealed significant differ¬ences among taxa and also among lines and races of maize. The hybrids between Z. mays ssp. mays x Z. mays ssp. mexicana (2n = 20). Z. diploperennis x Z. perennis (2n = 30). And Z. diploperennis x Z.perennis (2n = 40) showed DNA content intermediate between that of the parents. The number of chromosomal C-bands and the proportion of the genome comprising C-band hete-rochromatin were positively related to genome size. In the different lines and races of maize studied, there was a positive correlation between genome size and the inter¬val from germination to flowering. Octoploid Z. perennis (2n = 40) showed the smallest DNA content per basic genome and the smallest heterochromatic blocks, sug¬gesting that the DNA lost by this species consisted main¬ly of repetitive sequences. Considering that the extant species of Zea are tetraploid (2n = 20) and octoploid (2n = 40) and that the ancestral diploids are extinct, any consideration of the direction (increase or decrease) of the DNA change would be entirely speculative. The ex¬tant species could be the product of natural and artificial selection acting on different genotypic and nucleotypical constitutions at the diploid and or tetraploid levels. Key words: Zea species and hybrids - Cytogenetics -DNA content - Heterochromatin - C-banding