Universidad Nacional de La Plata
Distribution of C-banded bivalents in
--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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