LLAVALLOL, ARGENTINA

Universidad Nacional de La Plata

Distribution of C-banded bivalents in maize --Maria del Carmen Molina, Lidia Poggio and Carlos A. Naranjo Molina and Naranjo (Theor. Appl. Genet. 73:542-550, 1987) and Naranjo and Molina (MNL 61:62-63, 1987) have obtained cytological evidence supporting X=5 as a basic number of the genus Zea, and have suggested a hypothetical genomic constitution for the species and hybrids studied. These authors showed that in hexaploid hybrids (2n=30) forming 5 III + 5 II + 5I in meiosis, there is a tendency of A, C and B genomes to separate into trivalent, bivalent and univalent groups, respectively. Later, in several 2n=20 species of the genus, two spindles of five bivalents each have been observed in first metaphase (Molina, Naranjo and Poggio, MNL 62:74, 1988). Detailed studies in diplotene and diakinesis indicate also two groups of five bivalents. Moreover, in some of these cells, an asynchronous development of meiosis between groups was observed.

With the aim of analyzing the distribution of bivalents on the two spindles, C-banding with Giemsa was done (Giraldez et al., Z. Pflanzenzuchtg. 83:40-48, 1979). The material used was the Ever Green variety. In meiosis, this variety showed a total of five C-banded bivalents, and in all cells where double spindles were observed the distribution of the C-banded bivalents was two in one spindle and three in the other. The other two possible distributions (5-0 and 4-1) have never been observed.

These results suggest that 5-5 bivalent distribution in diakinesis and metaphase I is not random.


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