In our cytogenetic cross-mapping of maize and Tripsacum, a chromosome from Tripsacum has been isolated which appears to carry the pygmy locus in common with corn chromosome 6.
Pollen mother cells were stained by the customary methods and observed for chromosome relationships at pachytene, diakinesis, metaphase and anaphase stages of meiosis.
The Tripsacum chromosome has been isolated and identified in the disomic (20 + 2) condition. Analysis at pachytene shows that it corresponds to chromosome 10 of the Tripsacum genome with a total length of 27.9 u and an arm ratio of 3.3. The long arm has a conspicuous large knob. The Tripsacum chromosome, though intact in a few cells, in a majority of cases showed a deletion of one of the chromatids of the entire short arm, resulting in a univalent condition of that part of the chromosome, while the long arm remained as a bivalent. This occurred in at least 75% of the cells observed. The segmented short arm, being unstable, either folds back on itself or is seen sticking on to one or the other of the maize chromosomes with no specific preference or any real association.
Though this particular Tripsacum chromosome appears to have at least one gene in common with maize chromosome 6, the nucleolus organizer chromosome of maize, it did not show any real association with this chromosome, or with the nucleolus. Nor does it resemble the nucleolus organizer chromosomes of the Tripsacum complement in any of its morphological details.
The disomic plants are pollen sterile. Though the tassels were produced, stamens were not exserted and did not shed any pollen. The monosomic plants are semi-sterile.
Chandra V. Pasupuleti and Walton C. Galinat
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