| Discussion This technique has been used to investigate a range of grass chromosomes. Giemsa stained karyotypes have been produced for Secale, Triticum and some of its diploid and tetraploid relatives, and banding has been observed in Fescue, Agropyron, Elumus, Hordeum, and Avena. Several aspects of the technique require greater attention than do others. The length of time in the mono-bromonapthalene solution is important. During this phase of the technique the spindle is inhibited, and the chromosomes contract. Too long a treatment will result in overly contracted chromosomes and will obscure faint bands. Too short a treatment will not allow the easy recognition of individual chromosomes. The treatment is temperature sensitive and appears to be accomplished best at about 70o-72oF. The time in alcohol (stage 5B) has optimum values for different species, with a degradation of the staining occurring with divergence from the best time. The best time for wheat is between 1 1 /4 and 1 1 /2 hours, and rye requires 2 1/2 hours. The length of the Giemsa staining also should be adjusted so that alcohol decolorization is generally not required. The times used have ranged from as little as fifteen seconds to as long as one and a half minutes. As with all techniques used in identifying individual chromosomes, there are limitations to the relability of the data obtained. If it is possible to identify the chromosomes by other techniques, then the banding pattern can be assigned with certainly to that chromosome. For example, the satellited chromosomes are conspicuous in any case and thus their banding pattern is easily identified. It is better to construct karyotypes of species from single, whole cells rather than from assembling a number of individual chromosomes. By using a complete cells, each chromosome can be identified disomically and the possibility of confusion between similarly banded chromosomes is reduced. |
| P.S.: This contribution is reprinted from Research Bulletin 1012 of the University of Missouri College of Agriculture Experiment Station, May 1975. |
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